Litestar's AllowedHosts has a validation bypass due to unescaped regex metacharacters in configured host patterns

Exploitation

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

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-25479: 0.36% estimated exploitation activity in the next 30 days; percentile 29.64 (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 AllowedHosts host validation can be bypassed because configured host patterns are turned into regular expressions without escaping regex metacharacters (notably .). A configured allowlist entry like example.com can match exampleXcom Details In litestar.middleware.allowedhosts, allowlist entries are compiled into regex patterns in a way that allows regex metacharacters to retain special meaning (e.g., . matches any character). This enables a bypass where an attacker supplies a host that matches the regex but is not the intended literal hostname. PoC Server (pocallowedhostsserver.py) uvicorn pocallowedhostsserver:app --host 127.0.0.1 --port 8001 Client (pocallowedhostsclient.py) Expected (vulnerable behavior): Host: evil.com → 400 invalid host Host: exampleXcom → 200 ok (bypass) Impact Type: security control bypass (host allowlist) Who is impacted: apps relying on AllowedHosts to prevent Host header attacks (cache poisoning, absolute URL construction abuse, password reset link…

Published by the source

9 Feb 2026, 17:19 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-93ph-p7v4-hwh4

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-93ph-p7v4-hwh4

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# Patch Next advisory brief: CVE-2026-25479

Advisory: Litestar's AllowedHosts has a validation bypass due to unescaped regex metacharacters in configured host patterns
IDs: CVE-2026-25479, GHSA-93ph-p7v4-hwh4
Record: https://patchnext.com/advisories/cve-2026-25479 (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: Medium (CVSS 6.5)
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-93ph-p7v4-hwh4 (OSV record GHSA-93ph-p7v4-hwh4 lists affected ranges: PyPI litestar >=2.19.0 <2.20.0 (fixed))
- Verified: https://github.com/advisories/GHSA-93ph-p7v4-hwh4 (GitHub-reviewed advisory GHSA-93ph-p7v4-hwh4 lists affected ranges: PyPI litestar >=2.19.0 <=2.19.0)

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