CVE-2026-21438: webtransport-go Memory Exhaustion Attack Due To Vulnerability

MODERATE
Advisory Identifier: GHSA-2f2x-8mwp-p2gc
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CVSS 5.3
CWE-459 CWE-401
Published
Advisory Summary

CVE-2026-21438 is a MODERATE (CVSS 5.3) memory exhaustion attack due to vulnerability (CWE-459: Incomplete Cleanup) affecting webtransport-go libraries in the Go ecosystem. The issue involves memory exhaustion attack due to missing cleanup of streams map. Remediation is available by upgrading affected packages to version 0.10.0.

CVE-2026-21438 at a Glance

CVE Identifier CVE-2026-21438
GHSA Identifier GHSA-2f2x-8mwp-p2gc
Severity MODERATE
CVSS v3.1 Base Score 5.3
CWE Classification CWE-459: Incomplete Cleanup
Affected Product webtransport-go
Package Ecosystem Go
Published Date
Last Updated

Security Impact

CVSS: 5.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability Low (A:L)

How to Fix CVE-2026-21438

To remediate this vulnerability, upgrade all affected webtransport-go dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/quic-go/webtransport-go fixed: 0.10.0 
Upgrade github.com/quic-go/webtransport-go to 0.10.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/quic-go/webtransport-go

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-21438, inspect your project dependencies for webtransport-go:

inspect dependencies for github.com/quic-go/webtransport-go

Analyze the terminal output to locate any version of webtransport-go in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.10.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-459: Incomplete Cleanup, where the product does not properly "clean up" and remove temporary or supporting resources after they have been used. In webtransport-go, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## 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.

CVE-2026-21438 Affected webtransport-go Versions

1 component(s)
Fixed Versions:
0.10.0
Product / Package Ecosystem Affected Versions Fixed Version
github.com/quic-go/webtransport-go
golang/github.com/quic-go/webtransport-go
Go
< 0.10.0
0.10.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/quic-go/webtransport-go/security/advisories/GHSA-2f2x-8mwp-p2gc
NVD — CVE-2026-21438 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-21438
webtransport-go Source Repository REPOSITORY
https://github.com/quic-go/webtransport-go
webtransport-go Release RELEASE
https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0

Frequently Asked Questions

What is CVE-2026-21438?
CVE-2026-21438 is a security vulnerability in webtransport-go involving Memory Exhaustion Attack due to Missing Cleanup of Streams Map under CWE-459: Incomplete Cleanup.
Which webtransport-go versions are affected?
Affected versions include releases prior to 0.10.0 across affected packages: github.com/quic-go/webtransport-go.
What version fixes CVE-2026-21438?
Upgrading to 0.10.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/quic-go/webtransport-go affected?
Yes, github.com/quic-go/webtransport-go is affected in releases prior to 0.10.0. Upgrade your dependency to 0.10.0 or later.
What is the CVSS score of CVE-2026-21438?
CVE-2026-21438 has a CVSS v3.1 base score of 5.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
What CWE is associated with CVE-2026-21438?
CVE-2026-21438 is classified under CWE-459: Incomplete Cleanup (The product does not properly "clean up" and remove temporary or supporting resources after they have been used.).
How can I check Go dependencies for CVE-2026-21438?
Run the dependency tree command: 'inspect dependencies for github.com/quic-go/webtransport-go'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2f2x-8mwp-p2gc",
  "modified" : "2026-02-12T22:07:42Z",
  "published" : "2026-02-12T15:29:11Z",
  "aliases" : [ "CVE-2026-21438" ],
  "summary" : "webtransport-go: Memory Exhaustion Attack due to Missing Cleanup of Streams Map",
  "details" : "## Summary\nAn 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.\n\n## Details\nwebtransport-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.\n\nA 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.\n\n## The Fix\nwebtransport-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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/quic-go/webtransport-go"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.10.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.9.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/quic-go/webtransport-go/security/advisories/GHSA-2f2x-8mwp-p2gc"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-21438"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/quic-go/webtransport-go"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-401", "CWE-459" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-12T15:29:11Z",
    "nvd_published_at" : "2026-02-12T19:15:51Z"
  }
}