CVE-2026-21435
Denial of Service in webtransport-go via QUIC Flow Control Abuse
Publication date: 2026-02-12
Last updated on: 2026-02-19
Assigner: GitHub, Inc.
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| quic-go | webtransport-go | to 0.10.0 (exc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-400 | The product does not properly control the allocation and maintenance of a limited resource. |
Attack-Flow Graph
AI Powered Q&A
What immediate steps should I take to mitigate this vulnerability?
To mitigate this vulnerability, you should upgrade the webtransport-go library to version 0.10.0 or later.
The fix in version 0.10.0 introduces a short deadline for sending the WT_CLOSE_SESSION capsule. If the capsule cannot be sent within this deadline due to withheld flow control credit, the CONNECT stream is reset instead, preventing indefinite blocking and denial of service.
Can you explain this vulnerability to me?
CVE-2026-21435 is a denial of service vulnerability in the webtransport-go library, which implements the WebTransport protocol. Before version 0.10.0, an attacker could cause the WebTransport session closure to hang indefinitely by withholding QUIC flow control credit on the CONNECT stream. This prevents the transmission of the WT_CLOSE_SESSION capsule, which is necessary to properly close a session, causing the close operation to block and never complete.
How can this vulnerability impact me? :
This vulnerability can cause a denial of service by blocking the closure of WebTransport sessions indefinitely. An attacker can exploit this by withholding flow control credit, causing resources to be consumed unnecessarily and preventing sessions from closing properly. This can lead to resource exhaustion and degraded service availability.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
I don't know
How can this vulnerability be detected on my network or system? Can you suggest some commands?
I don't know