CVE-2026-5388 (GCVE-0-2026-5388)
Vulnerability from cvelistv5 – Published: 2026-08-23 13:34 – Updated: 2026-08-26 16:16
VLAI
EPSS
VEX
Title
justhtml before 1.15.0 Multiple Security Issues
Summary
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.
Severity
9.8 (Critical)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-26 16:07 UTC
CWE
- CWE-20 - Improper Input Validation
Assigner
VulnCheck
CNA
References
2 references
| URL | Tags |
|---|---|
| https://github.com/EmilStenstrom/justhtml/securit… | vendor-advisory |
| https://www.vulncheck.com/advisories/justhtml-bef… | third-party-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| EmilStenstrom | justhtml |
Affected:
0 , < 1.15.0
(semver)
Unaffected: 1.15.0 (semver) |
Date Public
2026-04-09 00:00
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