Critical · CVSS 9.8CVE-2026-5388GHSA-C9VM-HV86-F23R

justhtml before 1.15.0 Multiple Security IssuesCVE-2026-5388

Answer in brief

CVE-2026-5388 records a Critical severity (CVSS 9.8) vulnerability in justhtml before 1.15.0 Multiple Security Issues. The current sources do not mark it as known exploited. The current feed maps EmilStenstrom/justhtml (generic), justhtml (pypi). 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 26, 2026Source checked Oct 7, 2026First seen by HOL Aug 7, 2026Material review Aug 26, 2026

Upstream Advisory

Key facts

Risk: Critical · CVSS 9.8
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 9.8. 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), justhtml (pypi). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
EmilStenstrom/justhtmlgeneric	>=0 <1.15.0	1.15.0
justhtmlpypi	>=0 <1.15.0	1.15.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for EmilStenstrom/justhtml, justhtml.
Review the reported fix. Update EmilStenstrom/justhtml to 1.15.0; justhtml to 1.15.0 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 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 7, 2026

Sources and claim methodology

Upstream source description

justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass sanitization to inject active HTML and JavaScript — for example via encoded javascript: URLs, backslash-based relative URLs resolved as remote hosts, markup-breaking programmatic element/attribute names or HTML comments, raw </textarea> reintroduction through Markdown passthrough, or preserved <style>/<meta http-equiv=refresh>/<base href> tags in custom policies. Most custom-policy issues do not affect the default sanitize=True configuration; they primarily affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies/transform pipelines.

Quoted source text, attributed separately from HOL analysis.