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CVE-2026-115349GHSA-3q64-rw38-243v

Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing

lepture mistune
Open in ThreatlineRecord JSON
CVSS
8.7High
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.34%Chance of exploitation activity in the next 30 days, higher than 26% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in3.3.0Fixed versionCVE List
Published22 Oct 2026Updated 22 Oct 2026CVE List

What fixes it

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Description

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.

Text from CVE List

Affected versions 2

  • mistuneaffected: 3.0.0 before 3.3.0CVE List
  • mistuneunaffected: 3.3.0CVE List

References 2