Is CVE-2026-21438 in the CISA KEV catalog?

No. CVE-2026-21438 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-21438?

CVE-2026-21438 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2026-21438?

CVE-2026-21438 has an EPSS score of 0.37% (29th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-21438?

Upgrade webtransport-go to 0.10.0 or later.

CVE & CISA-KEV Catalog

CVE-2026-21438

MEDIUM

5.3

CVSS v3

NVD

Description

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.

CWE-401Missing Release of Memory (Memory Leak)CWE-459

How to fix

Remediation Available

webtransport-goNVD

Affected:< 0.10.0Fixed in:0.10.0CVE-2026-21438derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Exploit Intelligence

0.37%probability of exploitation in 30 days

29thpercentile

Low risk: more likely to be exploited than 29% of all known CVEs.

References

Vendor Advisory1

github.com

Release Notes1

github.com

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-02-19.