CVE-2026-21438: webtransport-go is an implementation of the WebTransport protocol

Q: How do I fix CVE-2026-21438?

webtransport-go: upgrade to 0.10.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-21438 being exploited?

CVE-2026-21438 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-21438 affect?

CVE-2026-21438 affects webtransport-go. Severity is medium (CVSS 5.3). webtransport-go is an implementation of the WebTransport protocol. Prior to 0.10.0, an attacker can cause unbounded memory consumption repeatedly creating and closing many WebTransport streams. Closed streams were not removed from an intern

Q: How urgent is CVE-2026-21438?

Priority 32/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-21438 is a medium-severity flaw (CVSS 5.3) affecting webtransport-go. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

webtransport-go is an implementation of the WebTransport protocol. Prior to 0.10.0, 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. This vulnerability is fixed in v0.10.0.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 65%)
CISA exploited list	No
Weakness	CWE-401, CWE-459
Published	2026-02-12
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: quic-go

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-02-12 19:15 UTCPublished CVE record published
2026-06-17 10:18 UTCUpdated Record last modified

quic-go webtransport-go UPGRADE

Affected: < 0.10.0

Fixed in: 0.10.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy webtransport-go || rpm -q webtransport-go || webtransport-go --version

2. UPGRADE to 0.10.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade webtransport-go

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade webtransport-go

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-21438?

webtransport-go: upgrade to 0.10.0. Exact commands for each OS are on this page.

Is CVE-2026-21438 being exploited?

CVE-2026-21438 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-21438 affect?

CVE-2026-21438 affects webtransport-go. Severity is medium (CVSS 5.3). webtransport-go is an implementation of the WebTransport protocol. Prior to 0.10.0, an attacker can cause unbounded memory consumption repeatedly creating and closing many WebTransport streams. Closed streams were not removed from an intern

How urgent is CVE-2026-21438?

Priority 32/100. Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-21435 MEDIUM 5.3 UPGRADE webtransport-go is an implementation of the WebTransport protocol
CVE-2026-21434 MEDIUM 5.3 UPGRADE webtransport-go is an implementation of the WebTransport protocol

References

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