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CVE-2026-5388— justhtml before 1.15.0 Multiple Security Issues

Quick assessment

Affected
EmilStenstrom justhtml
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

justhtml 在 1.15.0 版本之前存在多个安全问题，涉及 URL 清理辅助函数（clean_url_value 和 clean_url_in_js_string）、HTML 序列化、Markdown 透传（html_passthrough=True）以及几种自定义清理策略的边缘情况。根据配置的不同，攻击者可能绕过清理机制，注入活跃的 HTML 和 JavaScript 代码——例如，通过编码后的 javascript: URL、基于反斜杠的相对 URL（被解析为远程主机）、通过程序化元素/属性名称或 HT

CVSS 9.8 · Critical EPSS 0.34% · P27

Affected Version Matrix 2

VendorProduct Version RangeStatus
EmilStenstrom justhtml < 1.15.0 affected
1.15.0 unaffected
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I. Basic Information for CVE-2026-5388

Vulnerability Information
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Vulnerability Title
justhtml before 1.15.0 Multiple Security Issues
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
输入验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
EmilStenstrom justhtml 0 ~ 1.15.0 -

II. Public POCs for CVE-2026-5388

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 12260 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
In-depth vulnerability mechanism
Trigger conditions & impact
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Exploit chain & mitigation
POC zip download
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III. Intelligence Information for CVE-2026-5388

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Vendor Advisories for CVE-2026-5388 (2)

Same Patch Batch · EmilStenstrom · 2026-08-23 · 11 CVEs total

CVE-2026-7808 9.8 CRITICAL justhtml before 1.16.0 Multiple Security Issues via Sanitization
CVE-2026-8445 9.8 CRITICAL justhtml before 1.12.0 Sanitizer Bypass via Markdown
CVE-2026-9769 7.5 HIGH justhtml before 1.10.0 Denial of Service via deeply nested HTML
CVE-2026-4671 7.5 HIGH justhtml before 1.18.0 Denial of Service via CSS Selector
CVE-2026-77088 6.1 MEDIUM justhtml 0.9.0 through 1.21.0 Cross-Site Scripting via code-span
CVE-2026-74793 6.1 MEDIUM justhtml before 3.11.0 XSS via selectedcontent projection
CVE-2026-6827 6.1 MEDIUM justhtml before 1.17.0 Multiple Cross-Site Scripting Vulnerabilities
CVE-2026-8630 6.1 MEDIUM justhtml before 1.12.0 Mutation XSS via Raw Text Elements
CVE-2026-5751 6.1 MEDIUM justhtml before 1.14.0 Mutation XSS via custom sanitization policies
CVE-2026-5389 6.1 MEDIUM justhtml before 1.13.0 XSS via code fence breakout

IV. Related Vulnerabilities

Same product: justhtml
Same vendor: EmilStenstrom
Same weakness: CWE-20

V. Comments for CVE-2026-5388

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