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Under GODEBUG=fips140=only, Go < 1.26.3 fails every TLS handshake while generating the default X25519MLKEM768 key share (golang/go#78372): crypto/ecdh: use of X25519 is not allowed in FIPS 140-only mode so a FIPS-enforced client cannot reach the Defined Networking API at all. Pin the minimum toolchain to the first release with the upstream fix.
johnmaguire
approved these changes
Sep 8, 2026
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Problem
A client built with Go < 1.26.3 running under
GODEBUG=fips140=onlycannot complete any TLS handshake with the Defined Networking API:This is golang/go#78372: under
fips140=only, the TLS client still attempts to generate the default X25519MLKEM768 key share, which is hard-disabled in enforce mode. Fixed upstream in go1.26.3.Fix
Pin
go 1.26.3in go.mod so consumers (dnclient release builds) cannot silently produce FIPS-broken binaries with an older toolchain.Runtime workaround for binaries already built with an affected Go:
GODEBUG=fips140=only,tlsmlkem=0.Verification
go build ./...and full test suite pass on go1.26.3+.GOTOOLCHAIN=go1.26.0 go build ./...is now correctly refused by the go directive.GODEBUG=fips140=only(see https://github.com/DefinedNet/dnclient/pull/885).