CVE-2024-37891 is a medium-severity (CVSS 4.4) CWE-669 vulnerability in urllib3. A fix is available for urllib3 — see the affected versions and patch details below.
Proxy-Authorization request header isn't stripped during cross-origin redirects in urllib3
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2024-37891.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2024-37891 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
urllib3🐍urllib3Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
urllib3 is a user-friendly HTTP client library for Python. 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. We believe the number of usages affected by this advisory is low. It requires all of the following to be true to be exploited: 1. Setting the Proxy-Authorization header without using urllib3's built-in proxy support. 2. Not disabling HTTP redirects. 3. Either not using an HTTPS origin server or for the proxy or target origin to redirect to a malicious origin. Users are advised to update to either version 1.26.19 or version 2.2.2. Users unable to upgrade may use the Proxy-Authorization header with urllib3's ProxyManager, disable HTTP redirects using redirects=False when sending requests, or not user the Proxy-Authorization header as mitigations.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | urllib3 | all versions | 1.26.19pip install --upgrade 'urllib3==1.26.19' |
| 🐍PyPI | urllib3 | ≥ 2.0.0&&< 2.2.2 | 2.2.2pip install --upgrade 'urllib3==2.2.2' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for urllib3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update urllib3 to 1.26.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-37891 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2024-37891 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2024-37891. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
.egg-info packages, like urllib3-1.24.2-py3.6.egg-info, store only metadata such as package version and dependencies and do not contain any affected codebase.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Ansible Automation Platform 2.4 for RHEL 8 | python3x-urllib3-0:1.26.20-1.el8ap | RHSA-2024:6765 |
| Red Hat Ansible Automation Platform 2.4 for RHEL 8 | automation-controller-0:4.5.12-1.el8ap | RHSA-2024:7312 |
| Red Hat Developer Hub 1.3 on RHEL 9 | rhdh/rhdh-hub-rhel9:1.3-100 | RHBA-2024:7523 |
| Red Hat Enterprise Linux 8 | container-tools:rhel8-8100020240808093819.afee755d | RHSA-2024:5258 |
| Red Hat Enterprise Linux 8 | fence-agents-0:4.2.1-129.el8_10.4 | RHSA-2024:6309 |
| Red Hat Enterprise Linux 8 | python3.12-urllib3-0:1.26.19-1.el8_10 | RHSA-2024:8842 |
| Red Hat Enterprise Linux 8 | python3.11-urllib3-0:1.26.12-4.el8_10 | RHSA-2024:8843 |
| Red Hat Enterprise Linux 8 | resource-agents-0:4.9.0-54.el8_10.4 | RHSA-2024:6311 |
Frequently Asked Questions
Is CVE-2024-37891 in your dependencies?
O3 Security finds CVE-2024-37891 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.