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CVE-2026-44897VulnerabilityPublished Updated

Mistune: Prior to 3.2.1, HTMLRenderer.heading() builds the opening <hN> tag by string-concatenating the id attribute

Affects mistuneSource GCVE Database

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Authoritative record:CVE-2026-44897· Medium 6.1

Not known to be exploited · CVSS 6.1 Medium · fixed in 3.2.1 : update mistune when convenient.

Data as of 9 Nov 2026, 14:18 UTC

CVSS 3.1 base score
6.1Medium
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 3.2.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 26 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 9 Nov 2026.

What to do

Affected software

ProductAffectedFixed in
Ubuntu 26.10mistunepkg:deb/ubuntu/mistune?arch=source&distro=stonkingOther threatsAffected
  • =3.1.4-1
Fixed in–
Ubuntu 26.10mistune0pkg:deb/ubuntu/mistune0?arch=source&distro=stonkingOther threatsAffected
  • =0.8.4-6
Fixed in–
Ubuntu 26.04 LTSmistunepkg:deb/ubuntu/mistune?arch=source&distro=resoluteOther threatsAffected
  • =3.1.3-1
  • =3.1.4-1
Fixed in–
Ubuntu 25.10mistunepkg:deb/ubuntu/mistune?arch=source&distro=questingOther threatsAffected
  • =3.0.2-2
  • =3.1.3-1
Fixed in–
Ubuntu 25.10mistune0pkg:deb/ubuntu/mistune0?arch=source&distro=questingOther threatsAffected
  • =0.8.4-4
Fixed in–
Ubuntu 24.04 LTSmistunepkg:deb/ubuntu/mistune?arch=source&distro=nobleOther threatsAffected
  • =2.0.4-2
  • =3.0.2-1
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade Mistune to version 3.2.1 or later, where this vulnerability is fixed. No other mitigation is required as the fix properly sanitizes the id attribute in the HTMLRenderer.heading() method.

Description

Mistune versions prior to 3.2.1 have a vulnerability in the HTMLRenderer.heading() function where the id attribute is concatenated directly into the HTML without sanitization. This allows an attacker to inject arbitrary additional attributes into heading elements by including a double-quote character in the id value. The issue is fixed in version 3.2.1.

References

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