CVE-2026-4671
justhtml before 1.18.0 Denial of Service via CSS Selector
Description
justhtml before 1.18.0 contains multiple low-severity denial-of-service issues in CSS selector handling and linkification. Applications that evaluate attacker-controlled selector strings (via query(), matches(), or selector-based transforms), run selector matching over very large untrusted documents, construct DOM trees from untrusted structure, or enable linkification over attacker-controlled text may consume disproportionate CPU or memory. Triggers include oversized selectors, large selector lists, oversized compound selectors, long combinator chains, deeply nested functional pseudo-classes, repeated token/positional matching, cyclic DOM graphs causing non-terminating traversal, and punctuation-heavy or trailing-bracket linkification input. These are availability-only concerns and do not by themselves allow script execution, data disclosure, or sanitizer bypass. Default JustHTML(sanitize=True) usage is not expected to be exposed, since selectors are normally supplied by application code.
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-2026-4671
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 | HIGH | 83251b91-4cc7-4094-a5c7-464a1b83ea10 | ||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | MITRE-CVE | ||||
| CVSS 4.0 | HIGH | 83251b91-4cc7-4094-a5c7-464a1b83ea10 | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Update justhtml to version 1.18.0 or later.
- Review and sanitize CSS selector inputs.
- Limit processing of untrusted document content.
- Disable linkification for untrusted text.
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-2026-4671.
| URL | Resource |
|---|---|
| https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-r8cj-3554-33mr | |
| https://www.vulncheck.com/advisories/justhtml-before-denial-of-service-via-css-selector |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-4671 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-2026-4671
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-2026-4671 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-4671 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 1.18.0 contiene múltiples problemas de denegación de servicio de baja gravedad en el manejo de selectores CSS y la linkificación. Las aplicaciones que evalúan cadenas de selectores controladas por el atacante (a través de query(), matches() o transformaciones basadas en selectores), ejecutan la coincidencia de selectores sobre documentos no confiables muy grandes, construyen árboles DOM a partir de estructuras no confiables, o habilitan la linkificación sobre texto controlado por el atacante pueden consumir una cantidad desproporcionada de CPU o memoria. Los desencadenantes incluyen selectores de tamaño excesivo, listas de selectores grandes, selectores compuestos de tamaño excesivo, cadenas de combinadores largas, pseudoclases funcionales profundamente anidadas, coincidencia repetida de tokens/posicional, gráficos DOM cíclicos que causan un recorrido no terminante, y entrada de linkificación con mucha puntuación o corchetes finales. Estas son preocupaciones solo de disponibilidad y no permiten por sí mismas la ejecución de scripts, la divulgación de datos o la omisión del saneador. El uso predeterminado de JustHTML(sanitize=True) no se espera que esté expuesto, ya que los selectores son normalmente proporcionados por el código de la aplicación. -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 24, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-4671', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-08-24T18:08:58.030472Z'} -
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': '1.18.0', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '1.18.0', 'versionType': 'semver'}], 'packageURL': 'pkg:pypi/justhtml', 'defaultStatus': 'unaffected'}] Added Description justhtml before 1.18.0 contains multiple low-severity denial-of-service issues in CSS selector handling and linkification. Applications that evaluate attacker-controlled selector strings (via query(), matches(), or selector-based transforms), run selector matching over very large untrusted documents, construct DOM trees from untrusted structure, or enable linkification over attacker-controlled text may consume disproportionate CPU or memory. Triggers include oversized selectors, large selector lists, oversized compound selectors, long combinator chains, deeply nested functional pseudo-classes, repeated token/positional matching, cyclic DOM graphs causing non-terminating traversal, and punctuation-heavy or trailing-bracket linkification input. These are availability-only concerns and do not by themselves allow script execution, data disclosure, or sanitizer bypass. Default JustHTML(sanitize=True) usage is not expected to be exposed, since selectors are normally supplied by application code. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/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 Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-400 Added Reference https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-r8cj-3554-33mr Added Reference https://www.vulncheck.com/advisories/justhtml-before-denial-of-service-via-css-selector