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webtransport-go CloseWithError can block indefinitely

CVSS 3.1 5.3 MEDIUMEUVD CVSS 3.1 5.3 CVSS 3.1 · [email protected] · Secondary 5.3 MEDIUMCVSS 3.1 · [email protected] · Primary 7.5 HIGHCVSS_V3 Publisher rating MODERATEFixed by github.com/quic-go/webtransport-go 0.10.0osv · severity unknownFixed by github.com/quic-go/webtransport-go 0.10.0KEV status unknown

cve-program · CVE-2026-21435

Published

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.

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euvd · EUVD-2026-6717

Published

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.

Read the publisher's advisory

nvd · CVE-2026-21435

Published

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.

Read the publisher's advisory

osv · GHSA-px4r-g4p3-hhqv

Published

## Summary 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. ## Details WebTransport over HTTP/3 signals session termination by sending a WT_CLOSE_SESSION capsule on the CONNECT stream. The capsule is only needed to transmit a reason phrase and an error code to the peer. After the capsule is sent, the CONNECT stream is closed. In affected versions, the closure procedure blocked indefinitely while waiting for sufficient QUIC flow control credit from the peer. A malicious peer can withhold this credit, preventing the capsule from being sent. ## The Fix webtransport-go now attempts to send the WT_CLOSE_SESSION capsule with a short deadline. If the capsule cannot be sent within this deadline, the CONNECT stream is reset instead. This closes the WebTransport session promptly without transmitting the optional error details. This prevents indefinite blocking on session closure.

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osv · GO-2026-4488

Published

webtransport-go: CloseWithError can block indefinitely in github.com/quic-go/webtransport-go

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Affected versions, risk and source history

cve-program · CVE-2026-21435

Published

webtransport-go

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "quic-go",
                    "product": "webtransport-go",
                    "versions": [
                        {
                            "version": "< 0.10.0",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON

euvd · EUVD-2026-6717

Published

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Feb 12, 2026, 6:22:58 PM

dateUpdated: Feb 17, 2026, 3:36:08 PM

No normalized affected-package data is projected for this source revision. The original publisher record may contain additional product and version evidence; this does not establish that a package is unaffected.

Original source record · Cite this exact observation · Complete original publisher JSON

nvd · CVE-2026-21435

Published

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Analyzed

Weakness classifications: CWE-400

Original publisher date fields

published: 2026-02-12T19:15:51.503

lastModified: 2026-06-17T10:18:40.043

1 source CPE criteria · context only
  • cpe:2.3:a:quic-go:webtransport-go:*:*:*:*:*:go:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

No normalized affected-package data is projected for this source revision. The original publisher record may contain additional product and version evidence; this does not establish that a package is unaffected.

Original source record · Cite this exact observation · Complete original publisher JSON

osv · GHSA-px4r-g4p3-hhqv

Published

github.com/quic-go/webtransport-go

Go

SEMVER · introduced 0 → fixed 0.10.0

Original source record · Cite this exact observation · Complete original publisher JSON

osv · GO-2026-4488

Published

github.com/quic-go/webtransport-go

Go

SEMVER · introduced 0 → fixed 0.10.0

Original source record · Cite this exact observation · Complete original publisher JSON

ChangeIntel

An IT change radar: releases, security, known issues, retirements, documentation changes, and service status from public sources. Every item links to supporting evidence; dates and statuses can change after they are read.

Sources read 15 Nov 12:11 UTC · 256 of 275 readable · 252 fully read · documentation 469/469 current