CVE-2026-6827
justhtml before 1.17.0 Multiple Cross-Site Scripting Vulnerabilities
Description
justhtml before 1.17.0 contains multiple security issues in sanitization, serialization, and programmatic DOM handling. When custom policies preserve foreign namespaces (SVG/MathML), dangerous content such as HTML integration points (SVG <foreignObject>, MathML <annotation-xml encoding="text/html">) and mutation-XSS parser-differential payloads could survive sanitization and become active HTML after reparse; SVG filter="url(...)" and preserved <style> could leave resource-loading CSS (@import, background-image:url()). Programmatic script/style/Comment nodes could serialize into active markup. Additional hardening fixes address sanitize-pipeline cache mutation and DOM parent/child cycles that could cause infinite loops. Most issues affect advanced or custom configurations rather than the default JustHTML(..., sanitize=True) safe path.
INFO
Published Date :
Aug. 23, 2026, 2:16 p.m.
Last Modified :
Oct. 12, 2026, 4:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-6827
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | 83251b91-4cc7-4094-a5c7-464a1b83ea10 | ||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE | ||||
| CVSS 4.0 | MEDIUM | 83251b91-4cc7-4094-a5c7-464a1b83ea10 | ||||
| CVSS 4.0 | MEDIUM | [email protected] |
Solution
- Update JustHTML to version 1.17.0 or later.
- Review and update custom sanitization policies.
- Avoid preserving foreign namespaces in custom policies.
- Ensure programmatic nodes are properly sanitized.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-6827.
| URL | Resource |
|---|---|
| https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-vrx2-77f2-ww34 | |
| https://www.vulncheck.com/advisories/justhtml-before-multiple-cross-site-scripting-vulnerabilities |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-6827 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-6827
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-6827 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-6827 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Oct. 12, 2026
Action Type Old Value New Value Added Translation Title: justhtml de EmilStenstrom, Description: justhtml anterior a la versión 1.17.0 contiene múltiples problemas de seguridad en la sanitización, serialización y manejo programático del DOM. Cuando las políticas personalizadas preservan espacios de nombres externos (SVG/MathML), contenido peligroso como puntos de integración HTML (SVG <foreignObject>, MathML <annotation-xml encoding=“text/html”>) y cargas útiles de XSS por mutación con diferencias de analizador podrían sobrevivir a la sanitización y convertirse en HTML activo después de un nuevo análisis; SVG filter=“url(...)” y <style> preservado podrían dejar CSS de carga de recursos (@import, background-image:url()). Los nodos programáticos de script/style/Comment podrían serializarse en marcado activo. Correcciones de endurecimiento adicionales abordan la mutación de la caché de la tubería de sanitización y los ciclos padre/hijo del DOM que podrían causar bucles infinitos. La mayoría de los problemas afectan a configuraciones avanzadas o personalizadas en lugar de la ruta segura predeterminada de JustHTML(..., sanitize=True). -
CVE Modified by [email protected]
Aug. 29, 2026
Action Type Old Value New Value Added Affected Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/6xxx/CVE-2026-6827.json">CVE-2026-6827</a> -
CVE Modified by [email protected]
Aug. 26, 2026
Action Type Old Value New Value Added Reference https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-vrx2-77f2-ww34 Added Reference https://www.vulncheck.com/advisories/justhtml-before-multiple-cross-site-scripting-vulnerabilities Removed Reference https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-vrx2-77f2-ww34 Removed Reference https://www.vulncheck.com/advisories/justhtml-before-multiple-cross-site-scripting-vulnerabilities -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 26, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-6827', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-08-26T18:05:56.854604Z'} -
New CVE Received by [email protected]
Aug. 23, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'EmilStenstrom', 'product': 'justhtml', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '1.16.0', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '1.16.0', 'versionType': 'semver'}], 'packageURL': 'pkg:pypi/justhtml', 'defaultStatus': 'unaffected'}] Added Description justhtml before 1.17.0 contains multiple security issues in sanitization, serialization, and programmatic DOM handling. When custom policies preserve foreign namespaces (SVG/MathML), dangerous content such as HTML integration points (SVG <foreignObject>, MathML <annotation-xml encoding="text/html">) and mutation-XSS parser-differential payloads could survive sanitization and become active HTML after reparse; SVG filter="url(...)" and preserved <style> could leave resource-loading CSS (@import, background-image:url()). Programmatic script/style/Comment nodes could serialize into active markup. Additional hardening fixes address sanitize-pipeline cache mutation and DOM parent/child cycles that could cause infinite loops. Most issues affect advanced or custom configurations rather than the default JustHTML(..., sanitize=True) safe path. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/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 Added CVSS V3.1 AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Added CWE CWE-79 Added Reference https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-vrx2-77f2-ww34 Added Reference https://www.vulncheck.com/advisories/justhtml-before-multiple-cross-site-scripting-vulnerabilities