Litestar's CORS origin allowlist has a bypass due to unescaped regex metacharacters in allowed origins

Exploitation

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

CVSS

7.4 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N

EPSS

• CVE-2026-25478: 0.45% estimated exploitation activity in the next 30 days; percentile 38.82 (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 CORS origin validation can be bypassed because the allowed-origins allowlist is compiled into a regex without escaping metacharacters (notably .). An allowed origin like https://good.example can match https://goodXexample, resulting in Access-Control-Allow-Origin being set for an untrusted origin Details CORSConfig.allowedoriginsregex is constructed using a regex built from configured allowlist values and used with fullmatch() for validation. Because metacharacters are not escaped, a malicious origin can match unexpectedly. The check relies on allowedoriginsregex.fullmatch(origin). PoC Server (poccorsserver.py) uvicorn poccorsserver:app --host 127.0.0.1 --port 8002 Client (poccorsclient.py) Expected (vulnerable behavior): Origin: https://evil.example → no ACAO Origin: https://goodXexample → ACAO: https://goodxexample/ (bypass) Impact Type: CORS policy bypass (cross-origin data exposure risk) Who is impacted: apps using CORS allowlists to restrict browser cross-origin reads.…

Published by the source

9 Feb 2026, 17:18 UTC

Last modified by the source

13 Jul 2026, 07:26 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-2p2x-hpg8-cqp2

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-2p2x-hpg8-cqp2

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# Patch Next advisory brief: CVE-2026-25478

Advisory: Litestar's CORS origin allowlist has a bypass due to unescaped regex metacharacters in allowed origins
IDs: CVE-2026-25478, GHSA-2p2x-hpg8-cqp2
Record: https://patchnext.com/advisories/cve-2026-25478 (revision 2, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: litestar 2.20.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI litestar: affected >= 2.19.0, <= 2.19.0; fixed in 2.20.0

## Suggested inspection (read-only)
- `python -m pip show litestar`: 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 litestar.
- 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-2p2x-hpg8-cqp2 (OSV record GHSA-2p2x-hpg8-cqp2 lists affected ranges: PyPI litestar >=2.19.0 <2.20.0 (fixed))
- Verified: https://github.com/advisories/GHSA-2p2x-hpg8-cqp2 (GitHub-reviewed advisory GHSA-2p2x-hpg8-cqp2 lists affected ranges: PyPI litestar >=2.19.0 <=2.19.0)

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