Request smuggling leading to endpoint restriction bypass in Gunicorn

Exploitation

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

CVSS

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

EPSS

• CVE-2024-1135: 3.00% estimated exploitation activity in the next 30 days; percentile 87.36 (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.

Gunicorn fails to properly validate Transfer-Encoding headers, leading to HTTP Request Smuggling (HRS) vulnerabilities. By crafting requests with conflicting Transfer-Encoding headers, attackers can bypass security restrictions and access restricted endpoints. This issue is due to Gunicorn's handling of Transfer-Encoding headers, where it incorrectly processes requests with multiple, conflicting Transfer-Encoding headers, treating them as chunked regardless of the final encoding specified. This vulnerability has been shown to allow access to endpoints restricted by gunicorn. This issue has been addressed in version 22.0.0. To be affected users must have a network path which does not filter out invalid requests. These users are advised to block access to restricted endpoints via a firewall or other mechanism if they are unable to update.

Published by the source

16 Apr 2024, 00:30 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:35 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w3h3-4rj7-4ph4

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-w3h3-4rj7-4ph4

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# Patch Next advisory brief: CVE-2024-1135

Advisory: Request smuggling leading to endpoint restriction bypass in Gunicorn
IDs: CVE-2024-1135, GHSA-w3h3-4rj7-4ph4
Record: https://patchnext.com/advisories/cve-2024-1135 (revision 2, source checked 26 Oct 2026, 13:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: gunicorn 22.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI gunicorn: affected < 22.0.0; fixed in 22.0.0

## Suggested inspection (read-only)
- `python -m pip show gunicorn`: 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 gunicorn.
- 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-w3h3-4rj7-4ph4 (OSV record GHSA-w3h3-4rj7-4ph4 lists affected ranges: PyPI gunicorn >=0 <22.0.0 (fixed))
- Verified: https://github.com/advisories/GHSA-w3h3-4rj7-4ph4 (GitHub-reviewed advisory GHSA-w3h3-4rj7-4ph4 lists affected ranges: PyPI gunicorn >=0 <22.0.0)

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