SEPTEMBER 17, 2026
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Case File

CVE-2026-5388

CRITICAL · CVSS 9.8 EPSS 0.34% Public Exploit

Source: NVD + CISA KEV + EPSS · Published 2026-08-23 · Last synced 2026-09-17

CyberRota Analysis

AI-Generated

The vulnerability affects the justhtml library in Java, specifically in its URL sanitization and HTML serialization processes, allowing attackers to bypass security measures and inject malicious HTML and JavaScript. The impact can lead to cross-site scripting (XSS) attacks, potentially compromising user data and application integrity. Organizations using justhtml, particularly those with custom sanitization policies or relying on the html_passthrough feature, should prioritize remediation to mitigate these critical risks.

Public Exploit Signal

A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.

GitHub PoC Links

Note: these links are listed for security research and verification purposes only.

CVE
CVE-2026-5388
Severity
CRITICAL
CVSS
9.8
EPSS
0.34%
Java

Original NVD 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.