CVE-2026-4671justhtml before 1.18.0 Denial of Service via CSS Selector

Official 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.

Affected packages & fixed versions

Affected products (as reported)

References

• GitHub Security Advisory (GHSA-r8cj-3554-33mr) vendor-advisory
• VulnCheck Advisory: justhtml before 1.18.0 Denial of Service via CSS Selector third-party-advisory