Urllib3 Incorrect Certificate Validation

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2016-9015: 0.75% estimated exploitation activity in the next 30 days; percentile 55.13 (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.

Versions 1.17 and 1.18 of the Python urllib3 library suffer from a vulnerability that can cause them, in certain configurations, to not correctly validate TLS certificates. This places users of the library with those configurations at risk of man-in-the-middle and information leakage attacks. This vulnerability affects users using versions 1.17 and 1.18 of the urllib3 library, who are using the optional PyOpenSSL support for TLS instead of the regular standard library TLS backend, and who are using OpenSSL 1.1.0 via PyOpenSSL. This is an extremely uncommon configuration, so the security impact of this vulnerability is low.

Published by the source

17 May 2022, 03:05 UTC

Last modified by the source

18 Nov 2024, 23:23 UTC

Source last checked

26 Oct 2026, 13:27 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-v4w5-p2hg-8fh6

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-v4w5-p2hg-8fh6

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# Patch Next advisory brief: CVE-2016-9015

Advisory: Urllib3 Incorrect Certificate Validation
IDs: CVE-2016-9015, GHSA-v4w5-p2hg-8fh6
Record: https://patchnext.com/advisories/cve-2016-9015 (revision 3, source checked 26 Oct 2026, 13:27 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: urllib3 1.18.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI urllib3: affected >= 1.17, <= 1.18; fixed in 1.18.1

## Suggested inspection (read-only)
- `python -m pip show urllib3`: 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 urllib3.
- 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-v4w5-p2hg-8fh6 (OSV record GHSA-v4w5-p2hg-8fh6 lists affected ranges: PyPI urllib3 >=1.17 <1.18.1 (fixed))
- Verified: https://github.com/advisories/GHSA-v4w5-p2hg-8fh6 (GitHub-reviewed advisory GHSA-v4w5-p2hg-8fh6 lists affected ranges: PyPI urllib3 >=1.17 <=1.18)

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