CVE-2026-44899Public exploitNetwork attack vector

UI redressing via prefix-validated image dimensions

Published May 26, 2026 · Updated May 26, 2026

CSS injection in the Mistune Image directive before 3.2.1 allows remote attackers to create UI-redressing overlays via crafted dimensions. A prefix-only regular expression accepts width or height values beginning with digits, and render_block_image() copies the full value unescaped into an inline style attribute. Exploitation requires an application to enable the Image directive, render attacker-controlled Markdown to HTML, and present the result to a user; the injected CSS can obscure the page with a phishing overlay.

CVSS severity4.7
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

CSS injection in the Mistune Image directive before 3.2.1 allows remote attackers to create UI-redressing overlays via crafted dimensions. A prefix-only regular expression accepts width or height values beginning with digits, and render_block_image() copies the full value unescaped into an inline style attribute. Exploitation requires an application to enable the Image directive, render attacker-controlled Markdown to HTML, and present the result to a user; the injected CSS can obscure the page with a phishing overlay.

The record

CVE
CVE-2026-44899
Published
May 26, 2026
Updated
May 26, 2026
Vendor
Lepture
Product
Mistune
Classifications
CWE-79
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 26, 2026CVE publishedPublication date reported by the CVE source.
  2. May 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.2.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Lepture · Mistuneversion=< 3.2.1

Published CVSS scores

4.7GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo