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webtransport-go: Memory Exhaustion Attack due to Missing Cleanup of Streams Map

Moderate severity GitHub Reviewed Published Feb 12, 2026 in quic-go/webtransport-go • Updated Feb 12, 2026

Package

gomod github.com/quic-go/webtransport-go (Go)

Affected versions

<= 0.9.0

Patched versions

0.10.0

Description

Summary

An attacker can cause unbounded memory consumption repeatedly creating and closing many WebTransport streams. Closed streams were not removed from an internal session map, preventing garbage collection of their resources.

Details

webtransport-go maintains an internal map tracking WebTransport streams (both unidirectional and bidirectional) belonging to a session. In affected versions, entries for closed streams were not removed from this map, causing the map to grow indefinitely as streams were created and closed.

A malicious peer can exploit this by opening large numbers of streams and closing them, leading to steady memory growth proportional to the number of closed streams.

The Fix

webtransport-go now removes closed streams from the internal map upon closure. This allows the associated resources to be garbage collected, bounding memory usage to active streams only.

References

@marten-seemann marten-seemann published to quic-go/webtransport-go Feb 12, 2026
Published to the GitHub Advisory Database Feb 12, 2026
Reviewed Feb 12, 2026
Published by the National Vulnerability Database Feb 12, 2026
Last updated Feb 12, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(2nd percentile)

Weaknesses

Missing Release of Memory after Effective Lifetime

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse. Learn more on MITRE.

Incomplete Cleanup

The product does not properly clean up and remove temporary or supporting resources after they have been used. Learn more on MITRE.

CVE ID

CVE-2026-21438

GHSA ID

GHSA-2f2x-8mwp-p2gc

Source code

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