CVE-2026-5388

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.

CVSS v3 9.8 CRITICAL

9.8^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-c9vm-hv86-f23r
https://www.vulncheck.com/advisories/justhtml-before-multiple-security-issues

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-23 14:16

Updated : 2026-08-26 17:17

NVD link : CVE-2026-5388

Mitre link : CVE-2026-5388

CVE.ORG link : CVE-2026-5388

JSON object : View

Products Affected

No product.

CWE

CWE-20

Improper Input Validation

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