Python Liquid: Infinite loop when parsing malformed {% case %} tags

Exploitation

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

CVSS 4.0

5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-55865: 0.45% estimated exploitation activity in the next 30 days; percentile 39.23 (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.

Impact Given a malformed {% case %} tag without associated {% when %} or {% else %} block, and no terminating {% endcase %} tag, Python Liquid hangs in an infinite loop at parse time. This allows malicious template authors to craft templates for a denial of service attack. Patches The issue is fixed in version 2.2.1 with the correction of the liquid.TokenStream.eof attribute. The kind and value of the special EOF token are now the same, so either can be tested against liquid.token.TOKENEOF. Workarounds Manually correct the definition of liquid.TokenStream.eof before parsing any templates.

Published by the source

19 Jun 2026, 20:46 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:46 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vq2f-vcc9-j8mv

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-vq2f-vcc9-j8mv

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# Patch Next advisory brief: CVE-2026-55865

Advisory: Python Liquid: Infinite loop when parsing malformed `{% case %}` tags
IDs: CVE-2026-55865, GHSA-vq2f-vcc9-j8mv
Record: https://patchnext.com/advisories/cve-2026-55865 (revision 3, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: python-liquid 2.2.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI python-liquid: affected < 2.2.1; fixed in 2.2.1

## Suggested inspection (read-only)
- `python -m pip show python-liquid`: 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 python-liquid.
- 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-vq2f-vcc9-j8mv (OSV record GHSA-vq2f-vcc9-j8mv lists affected ranges: PyPI python-liquid >=0 <2.2.1 (fixed))
- Verified: https://github.com/advisories/GHSA-vq2f-vcc9-j8mv (GitHub-reviewed advisory GHSA-vq2f-vcc9-j8mv lists affected ranges: PyPI python-liquid >=0 <2.2.1)

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