CVE-2026-21435: webtransport-go: CloseWithError can block indefinitely

February 12, 2026

An attacker can cause a denial of service in webtransport-go by preventing or indefinitely delaying WebTransport session closure. A malicious peer can withhold QUIC flow control credit on the CONNECT stream, blocking transmission of the WT_CLOSE_SESSION capsule and causing the close operation to hang.

References

github.com/advisories/GHSA-px4r-g4p3-hhqv
github.com/quic-go/webtransport-go
github.com/quic-go/webtransport-go/releases/tag/v0.10.0
github.com/quic-go/webtransport-go/security/advisories/GHSA-px4r-g4p3-hhqv
nvd.nist.gov/vuln/detail/CVE-2026-21435

Code Behaviors & Features

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