Vulnerability in justhtml (CVE-2026-4671)

Summary

justhtml 1.18.0 fixes multiple low-severity denial-of-service hardening issues in CSS selector handling and linkification.

These issues are availability concerns. They do not allow script execution, data disclosure, or sanitizer bypass by themselves.

Affected versions

• justhtml < 1.18.0

Fixed version

• justhtml 1.18.0 released on May 4, 2026

Impact

CSS selector handling

Applications that evaluate attacker-controlled selector strings, or that run selector-based transform pipelines over attacker-controlled documents, could consume disproportionate CPU or memory.

The affected selector patterns included oversized selectors, large selector lists, oversized compound selectors, long combinator chains, deeply nested functional pseudo-classes such as :not(...), repeated attribute/class token matching over large values, repeated sibling or ancestor scans, repeated positional pseudo-class work, and :contains(...) over large descendant text.

Programmatically constructed malformed DOM graphs could also trigger non-terminating or duplicate traversal in some selector paths, including cyclic/shared child graphs, cyclic parent chains, and cyclic text traversal for :contains(...).

Linkification

Attacker-controlled text containing punctuation-heavy input or URL candidates ending in long runs of unmatched closing brackets could cause repeated rescanning and consume disproportionate CPU when linkification was enabled.

Default configu…