justhtml before 1.13.0 XSS via code fence breakout (CVE-2026-5389) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-5389

justhtml before 1.13.0 XSS via code fence breakout

Answer in brief

CVE-2026-5389 records a Unknown severity vulnerability in justhtml before 1.13.0 XSS via code fence breakout. The current sources do not mark it as known exploited. The current feed maps EmilStenstrom/justhtml (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 23, 2026Updated Aug 23, 2026Source checked Aug 23, 2026First seen by HOL Aug 23, 2026Material review Aug 23, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps EmilStenstrom/justhtml (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
EmilStenstrom/justhtmlgeneric	>=0 <1.13.0	1.13.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for EmilStenstrom/justhtml.
Review the reported fix. Update EmilStenstrom/justhtml to 1.13.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 23, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 23, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 23, 2026

Sources and claim methodology

Upstream source description

justhtml versions before 1.13.0 contain a cross-site scripting vulnerability in the to_markdown() function when serializing attacker-controlled pre content. Attackers can place backticks inside sanitized pre elements to break out of fixed-length code fences, allowing raw HTML to execute when the generated Markdown is rendered by CommonMark or GFM-style renderers.

Quoted source text, attributed separately from HOL analysis.