CVE-2026-21435

Name: CVE-2026-21435
Creator: NVD / NIST
Published: 2026-02-12T19:15:51.503+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 0.41%

Last modified Jun 17, 2026

CVE-2026-21435 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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. EPSS estimates a 0.41% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.41%

33.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-400

Affected Software

Vendor	Product	Versions
Quic-Go	Webtransport-Go	< 0.10.0

References

https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0Product, Release Notes
https://github.com/quic-go/webtransport-go/security/advisories/GHSA-px4r-g4p3-hhqvVendor Advisory

Timeline

Published: Feb 12, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-21435?

How severe is CVE-2026-21435?

CVE-2026-21435 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.41% probability of exploitation in the next 30 days.

How do I fix CVE-2026-21435?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-21435?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST