CVE-2026-121438

medium

Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying bal…

Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link 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 _contains_nested_link scans that exhaust CPU in parsing applications.

CVSS

5.3

5.3 (CVSS v3.1)

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

Severity source: NVD CVSS v3.1 (disclosure@vulncheck.com)

Timeline (UTC)

Published: 2026-11-03 15:17

Modified: 2026-11-03 15:17

NVD status: Deferred

Last synced 1 day ago

Verified against the source API 2026-11-03 15:20 UTC

Exploitation

Not listed in CISA KEV (as of last catalog sync)

Absence from KEV does not mean a CVE is not exploited. Exploitation status: unknown (no authoritative evidence in our sources).

Affected products

Not reported by the source (unknown — not "none").

Weakness classification (CWE)

CWE-400

Source: NVD / CISA. “NVD-CWE-Other” and “NVD-CWE-noinfo” mean NVD could not assign a specific weakness.

Mitigation & advisories

No vendor advisory or patch reference tagged by NVD. Check the references below.

References

https://github.com/lepture/mistune/commit/fe02f40faf091f86da9ed62c865f31e11da111d7 disclosure@vulncheck.com
https://github.com/lepture/mistune/security/advisories/GHSA-47p6-w2rc-5qf7 disclosure@vulncheck.com
https://www.vulncheck.com/advisories/mistune-before-3.3.3-denial-of-service-via-balanced-b... disclosure@vulncheck.com

Data sources

NVD CVE API 2.0 — fetched 2026-11-03 15:20 UTC · record ↗

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