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8.7

justhtml Denial-of-Service Vulnerability Fixed

published 11 days ago
Summary

justhtml versions before 1.18.0 may consume excessive system resources if given certain types of input, potentially causing performance issues. This issue affects applications that use justhtml to process CSS selectors or linkify text. To fix this, update to version 1.18.0 or later.

What to do
  • Update justhtml to version 1.18.0.
  • Update emilstenstrom justhtml to version 1.18.0 or later.
Affected software
Ecosystem VendorProductAffected versions
PyPI justhtml < 1.18.0
Fix: upgrade to 1.18.0
emilstenstrom justhtml < 1.18.0
Original advisory text
justhtml before 1.18.0 Denial of Service via CSS Selector
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.
Severity
8.7 High
Type
CWE-400Uncontrolled Resource Consumption
CWE-407Inefficient Algorithmic Complexity
CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
Timeline
Published23 Aug 2026
Updated24 Aug 2026
First seen8 May 2026
Sources
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