Gunicorn contains Improper Neutralization of CRLF sequences in HTTP headers

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2018-1000164: 2.37% estimated exploitation activity in the next 30 days; percentile 83.84 (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 version 19.4.5 contains a CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers vulnerability in "processheaders" function in "gunicorn/http/wsgi.py" that can result in an attacker causing the server to return arbitrary HTTP headers. This vulnerability appears to have been fixed in 19.5.0.

Published by the source

12 Jul 2018, 20:30 UTC

Last modified by the source

8 Sep 2026, 15:46 UTC

Source last checked

26 Oct 2026, 13:51 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-32pc-xphx-q4f6

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-32pc-xphx-q4f6

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# Patch Next advisory brief: CVE-2018-1000164

Advisory: Gunicorn contains Improper Neutralization of CRLF sequences in HTTP headers
IDs: CVE-2018-1000164, GHSA-32pc-xphx-q4f6
Record: https://patchnext.com/advisories/cve-2018-1000164 (revision 3, source checked 26 Oct 2026, 13:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: gunicorn 19.5.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI gunicorn: affected < 19.5.0; fixed in 19.5.0

## 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-32pc-xphx-q4f6 (OSV record GHSA-32pc-xphx-q4f6 lists affected ranges: PyPI gunicorn >=0 <19.5.0 (fixed))
- Verified: https://github.com/advisories/GHSA-32pc-xphx-q4f6 (GitHub-reviewed advisory GHSA-32pc-xphx-q4f6 lists affected ranges: PyPI gunicorn >=0 <19.5.0)

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