justhtml introduces denial-of-service hardening

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

not scored

EPSS

• CVE-2026-4671: 0.65% estimated exploitation activity in the next 30 days; percentile 51.28 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

8 May 2026, 18:19 UTC

Last modified by the source

24 Aug 2026, 03:55 UTC

Source last checked

26 Oct 2026, 13:41 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-r8cj-3554-33mr

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-r8cj-3554-33mr

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# Patch Next advisory brief: CVE-2026-4671

Advisory: justhtml introduces denial-of-service hardening
IDs: CVE-2026-4671, GHSA-r8cj-3554-33mr
Record: https://patchnext.com/advisories/cve-2026-4671 (revision 2, source checked 26 Oct 2026, 13:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: justhtml 1.18.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI justhtml: affected < 1.18.0; fixed in 1.18.0

## Suggested inspection (read-only)
- `python -m pip show justhtml`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on justhtml.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-r8cj-3554-33mr (OSV record GHSA-r8cj-3554-33mr lists affected ranges: PyPI justhtml >=0 <1.18.0 (fixed))
- Verified: https://github.com/advisories/GHSA-r8cj-3554-33mr (GitHub-reviewed advisory GHSA-r8cj-3554-33mr lists affected ranges: PyPI justhtml >=0 <1.18.0)

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