Vulnerability · Published Feb 12, 2026 · Assigned by GitHub_M

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

Medium 5.3

In plain English

A medium-severity uncontrolled resource consumption in webtransport-go from quic-go. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium

Exploit odds (30 days)0.5%top 59.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

webtransport-go is an implementation of the WebTransport protocol. Prior to v0.10.0, 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. This vulnerability is fixed in v0.10.0.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/quic-go/webtransport-go	0.10.0	GHSA-px4r-g4p3-hhqv
Go	github.com/quic-go/webtransport-go	0.10.0	GO-2026-4488

Affected products (as reported)

Vendor	Product	Versions
quic-go	webtransport-go	< 0.10.0

Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

https://github.com/quic-go/webtransport-go/security/advisories/GHSA-px4r-g4p3-hhqv x_refsource_CONFIRM
https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0 x_refsource_MISC