urllib3's Proxy-Authorization request header isn't stripped during cross-origin redirects
When using urllib3's proxy support with ProxyManager, the Proxy-Authorization header is only sent to the configured proxy, as expected.
However, when sending HTTP requests without using urllib3's proxy support, it's possible to accidentally configure the Proxy-Authorization header even though it won't have any effect as the request is not using a forwarding proxy or a tunneling proxy. In those cases, urllib3 doesn't treat the Proxy-Authorization HTTP header as one carrying authentication material and thus doesn't strip the header on cross-origin redirects.
Because this is a highly unlikely scenario, we believe the severity of this vulnerability is low for almost all users. Out of an abundance of caution urllib3 will automatically strip the Proxy-Authorization header during cross-origin redirects to avoid the small chance that users are doing this on accident.
Users should use urllib3's proxy support or disable automatic redirects to achieve safe processing of the Proxy-Authorization header, but we still decided to strip the header by default in order to further protect users who aren't using the correct approach.
Affected usages
We believe the number of usages affected by this advisory is low. It requires all of the following to be true to be exploited:
- Setting the
Proxy-Authorizationheader without using urllib3's built-in proxy support. - Not disabling HTTP redirects.
- Either not using an HTTPS origin server or for the proxy or target origin to redirect to a malicious origin.
Remediation
- Using the
Proxy-Authorizationheader with urllib3'sProxyManager. - Disabling HTTP redirects using
redirects=Falsewhen sending requests. - Not using the
Proxy-Authorizationheader.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | urllib3 | < 1.26.19, >= 2.0.0, < 2.2.2 | 1.26.19, 2.2.2 |
References
- https://github.com/urllib3/urllib3/security/advisories/GHSA-34jh-p97f-mpxf
- https://nvd.nist.gov/vuln/detail/CVE-2024-37891
- https://github.com/urllib3/urllib3/commit/40b6d1605814dd1db0a46e202d6e56f2e4c9a468
- https://github.com/urllib3/urllib3/commit/accff72ecc2f6cf5a76d9570198a93ac7c90270e
- https://github.com/urllib3/urllib3
- https://lists.debian.org/debian-lts-announce/2024/12/msg00020.html
- https://security.netapp.com/advisory/ntap-20240822-0003
- https://www.vicarius.io/vsociety/posts/proxy-authorization-header-handling-vulnerability-in-urllib3-cve-2024-37891
- https://pypi.org/project/urllib3
- https://github.com/advisories/GHSA-34jh-p97f-mpxf
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N- Weakness (CWE)
CWE-669- Platform
- Python (PyPI)
- Package
urllib3- Disclosed
- 17.06.2024
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1995 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-34jh-p97f-mpxf - CC BY 4.0
Vulnerability history: urllib3
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 22
- First → latest
- 01.2017 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 11
- Medium 10
Disclosures per year
- 2017: 1
- 2018: 1
- 2019: 2
- 2020: 2
- 2021: 2
- 2022: 0
- 2023: 3
- 2024: 1
- 2025: 4
- 2026: 6
-
urllib3's Proxy-Authorization request header isn't stripped during cross-origin redirects this entry
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.