Vulnerability · Published Oct 22, 2026 · Assigned by VulnCheck

CVE-2026-115351Mistune 3.2.1 before 3.3.0 CSS Injection via Figure Directive figwidth Option

Medium 4.7

In plain English

A medium-severity code injection in mistune from lepture. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities).

Severity (CVSS 3.1)4.7Medium

Exploit odds (30 days)0.2%top 87.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Mistune from 3.2.1 before 3.3.0 contains a CSS injection vulnerability that allows attackers controlling markdown input to inject arbitrary style declarations via the unvalidated figwidth option of the figure directive. Attackers can append declarations like background:url() to the rendered figure style attribute, forcing victim browsers to send requests to attacker servers and leak attribute values.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	mistune	no fix listed	DEBIAN-CVE-2026-115351
Debian:13	mistune	no fix listed	DEBIAN-CVE-2026-115351
Debian:14	mistune	no fix listed	DEBIAN-CVE-2026-115351
Ubuntu:22.04:LTS	mistune	no fix listed	UBUNTU-CVE-2026-115351
Ubuntu:24.04:LTS	mistune	no fix listed	UBUNTU-CVE-2026-115351
Ubuntu:26.04:LTS	mistune	no fix listed	UBUNTU-CVE-2026-115351
Ubuntu:26.10	mistune	no fix listed	UBUNTU-CVE-2026-115351

Affected products (as reported)

Vendor	Product	Versions
lepture	mistune	3.2.1 – before 3.3.0

Weakness: CWE-94 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N

References

GitHub Security Advisory (GHSA-xmwc-wjpr-q378) vendor-advisory
VulnCheck Advisory: Mistune 3.2.1 before 3.3.0 CSS Injection via Figure Directive figwidth Option third-party-advisory