EUVD-2026-64652
GHSA-9ph2-9r4x-rhjp
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Sanitizer-bypass XSS: attacker-supplied input (PR:N) but exploitation depends on non-default helpers/policies (AC:H) and a victim rendering content (UI:R); injected script crosses into the browser context (S:C) with limited C/I impact and no direct availability effect.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
4DescriptionCVE.org
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.
AnalysisAI
Sanitization bypass in justhtml (a Python HTML/Markdown sanitization library) before 1.15.0 lets attacker-controlled input reintroduce active HTML and JavaScript, resulting in cross-site scripting in consuming web applications. The flaws span URL-sanitization helpers, HTML serialization, Markdown passthrough, and custom policies - most do NOT affect the default sanitize=True path but do affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies. …
Unlock full vulnerability intelligence
- Risk assessment & exploitation conditions
- Attack chain visualization
- Remediation with exact patch versions
- Threat intelligence from 22 sources
- Personal watchlist & email alerts
Free forever · No credit card required
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the consuming application to use one of the affected code paths - specifically: the URL helper APIs JustHTML.clean_url_value()/clean_url_in_js_string(); programmatic DOM/element/attribute construction; Markdown rendering with to_markdown(html_passthrough=True); or custom sanitization policies / transform pipelines (e.g. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H) yields 9.3 (critical), but this appears to be a worst-case rating that assumes an application exercising the vulnerable code paths; it materially overstates risk for the common case. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A web application uses justhtml's clean_url_value helper (or html_passthrough=True Markdown rendering) to sanitize user-submitted profile bios. An attacker submits a bio containing an entity-encoded 'javascript:...' URL or a raw </textarea> break; the sanitizer accepts it as safe, and when another user views the profile the injected script executes in their browser, enabling session theft or actions on their behalf. … |
| Remediation | Vendor-released patch: upgrade justhtml to 1.15.0 (or later) via pip; this is the primary and complete fix per GHSA-c9vm-hv86-f23r. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all internal applications and services using justhtml and document their current versions. …
Sign in for detailed remediation steps and compensating controls.
Threat intelligence, references, and detailed analysis are available after sign-in.
Uncontrolled recursion in the justhtml Python HTML parsing library (all versions through 1.9.1) allows any remote unauth
Sanitizer bypass in the justhtml Python library (versions <= 1.11.0) allows attacker-controlled input to survive as raw
Cross-site scripting via HTML sanitization bypass affects justhtml (a Python HTML parsing/sanitization library by EmilSt
Uncontrolled resource consumption in justhtml before 1.18.0 enables denial-of-service conditions through CPU and memory
Cross-site scripting in justhtml 0.9.0-1.21.0 allows an attacker who can control the text content of HTML code or pre el
Cross-site scripting in justhtml before 3.11.0 allows remote unauthenticated attackers to execute arbitrary JavaScript i
Mutation XSS in justhtml (versions ≤1.11.0) allows injection of arbitrary HTML into serialized output when applications
Mutation XSS (mXSS) in justhtml 1.13.0 and earlier enables markup injection bypass against applications using non-defaul
Cross-site scripting in justhtml versions before 1.13.0 allows attackers who control `<pre>` element content to break ou
Sanitization bypass in justhtml (Python HTML sanitization library) before version 1.17.0 enables cross-site scripting in
Same weakness CWE-20 – Improper Input Validation
View allSame technique Authentication Bypass
View allShare
External POC / Exploit Code
Leaving vuln.today