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Vulnerabilities

Vulnerability · CVE-2026-33079

In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in that allows an attacker who can supply Markdown…

Published May 6, 2026 · catalog updated Aug 28, 2026 · the affected product

Last checked Oct 25, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-33079. EPSS is 0.53%. Act only if a listed version of the affected product is installed.

Gaps on this record

  • No plain product name is stored. The page cannot tell you which product to check.
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High8.7
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.53%
Remediation
Advisory link
Affected products
See sources for product scope

In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in that allows an attacker who can supply Markdown for parsing to cause denial of service. The regular expression used for parsing link titles contains overlapping alternatives that can trigger catastrophic backtracking. In both the double-quoted and single-quoted branches, a backslash followed by punctuation can be matched either as an escaped punctuation sequence or as two ordinary characters, creating an ambiguous pattern inside a repeated group. If an attacker supplies Markdown containing repeated ! sequences with no closing quote, the regex engine explores an exponential number of backtracking paths. This is reachable through normal Markdown parsing of inline links and block link reference definitions. A small crafted input can therefore cause significant CPU consumption and make applications using Mistune unresponsive.

No affected version ranges are stored yet. Use the vendor advisory before you decide this record does not apply.

How to fix CVE-2026-33079

  • No stored fix

    No vendor fix text is stored. Use the linked advisory before you change production.

  • Version check

    No version range is stored, so an installed version cannot be checked on this page.

  • Advisory

    Open the cve_org record and follow its fix.

  • Official advisories

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-33079. EPSS is 0.53%. Act only if a listed version of the affected product is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-1333: Inefficient Regular Expression Complexity. EPSS 0.53%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. May 6, 2026 · NIST NVD

    Detected

    In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in that allows an attacker who can supply Markdown for parsing to cause denial of service. The regular expression used for parsing link titles contains overlapping alternatives that can trigger catastrophic backtracking. In both the double-quoted and single-quoted branches, a backsla

  2. Aug 28, 2026 · NIST NVD

    Updated

    In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in that allows an attacker who can supply Markdown for parsing to cause denial of service. The regular expression used for parsing link titles contains overlapping alternatives that can trigger catastrophic backtracking. In both the double-quoted and single-quoted branches, a backsla

Sources

  • CVE.orgVulnerability recordCVE-2026-33079

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-33079

    30-day exploitation probability 0.53%

    first.org
  • NIST NVDVulnerability recordCVE-2026-33079

    In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in that allows an attacker who can supply Markdown for parsing to cause denial of service. The regular expression used for parsing link titles conta

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 25, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSOct 25, 2026
  • NIST NVDOct 20, 2026
  • CVE.orgOct 16, 2026