CVE-2026-21435 is a denial-of-service vulnerability in webtransport-go, an implementation of the WebTransport protocol, affecting versions prior to v0.10.0. A malicious peer can exploit this by withholding QUIC flow control credit, preventing the transmission of a session closure capsule and causing the close operation to hang indefinitely. Rated 7.5 HIGH on CVSS, this vulnerability has a network attack vector, low attack complexity, and can lead to a complete denial of service. There is currently no public exploit code available, nor is it listed in CISA's KEV catalog, though it has received some community discussion and media coverage.
| Vendor | Product | Version(s) | CPE |
|---|---|---|---|
< 0.10.0CPE matchmatch criteria | cpe:2.3:a:quic-go:webtransport-go:*:*:*:*:*:go:*:* |
CVSS version used by this source: 3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.
The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.