Is there a public exploit for CVE-2026-121438?

No public exploit for CVE-2026-121438 was found in Exploit-DB, Metasploit, Nuclei templates or public proof-of-concept repositories. That is an absence of evidence rather than proof that none exists.

How severe is CVE-2026-121438?

CVE-2026-121438 scores CVSS 6.9 (v4.0), rated medium.

What does CVE-2026-121438 affect?

CVE-2026-121438 affects lepture mistune.

6.9 Medium

Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parselink that allows attackers to cause quadratic CPU…

CVE-2026-121438

Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parselink that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of nested bracket pairs not forming a valid link, triggering repeated containsnestedlink scans that exhaust CPU in parsing applications.

Assessment

CVSS: 6.9 (v4.0)
Severity: Medium
Known exploited: Not listed in CISA KEV
Exploit availability: Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published: 3 November 2026
Last updated: 3 November 2026
Affected: lepture · mistune
Assigner: VulnCheck

CVSS vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

At the source

EUVD (ENISA)

References

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