---
id: CVE-2024-37891
aliases:
  - GHSA-34jh-p97f-mpxf
  - PYSEC-2026-1995
title: >-
  urllib3's Proxy-Authorization request header isn't stripped during
  cross-origin redirects
summary: >-
  urllib3's Proxy-Authorization request header isn't stripped during
  cross-origin redirects
severity: medium
cvss: 4.4
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N'
vendor: urllib3
product: urllib3
ecosystem: pip
affected:
  - urllib3 < 1.26.19
  - 'urllib3 >= 2.0.0, < 2.2.2'
patched:
  - urllib3 1.26.19
  - urllib3 2.2.2
published: '2024-06-17'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:14.811193644Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-34jh-p97f-mpxf'
references:
  - url: 'https://github.com/urllib3/urllib3/security/advisories/GHSA-34jh-p97f-mpxf'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2024-37891'
  - url: >-
      https://github.com/urllib3/urllib3/commit/40b6d1605814dd1db0a46e202d6e56f2e4c9a468
  - url: >-
      https://github.com/urllib3/urllib3/commit/accff72ecc2f6cf5a76d9570198a93ac7c90270e
  - url: 'https://github.com/urllib3/urllib3'
  - url: 'https://lists.debian.org/debian-lts-announce/2024/12/msg00020.html'
  - url: 'https://security.netapp.com/advisory/ntap-20240822-0003'
  - url: >-
      https://www.vicarius.io/vsociety/posts/proxy-authorization-header-handling-vulnerability-in-urllib3-cve-2024-37891
tags:
  - osv
  - pip
epss: 0.01141
epssPercentile: 0.65267
ingestedAt: '2026-07-08T18:25:44.668Z'
---

## Overview

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-Authorization` header 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-Authorization` header with urllib3's `ProxyManager`.
* Disabling HTTP redirects using `redirects=False` when sending requests.
* Not using the `Proxy-Authorization` header.

## Affected packages

- `urllib3 < 1.26.19`
- `urllib3 >= 2.0.0, < 2.2.2`

## Remediation

Upgrade to a patched release:

- `urllib3 1.26.19`
- `urllib3 2.2.2`