urllib3's request body not stripped after redirect from 303 status changes request method to GET

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2023-45803: 0.59% estimated exploitation activity in the next 30 days; percentile 48.39 (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.

urllib3 previously wouldn't remove the HTTP request body when an HTTP redirect response using status 303 "See Other" after the request had its method changed from one that could accept a request body (like POST) to GET as is required by HTTP RFCs. Although the behavior of removing the request body is not specified in the section for redirects, it can be inferred by piecing together information from different sections and we have observed the behavior in other major HTTP client implementations like curl and web browsers. From RFC 9110 Section 9.3.1: A client SHOULD NOT generate content in a GET request unless it is made directly to an origin server that has previously indicated, in or out of band, that such a request has a purpose and will be adequately supported. Affected usages Because the vulnerability requires a previously trusted service to become compromised in order to have an impact on confidentiality we believe the exploitability of this vulnerability is low. Additionally,…

Published by the source

17 Oct 2023, 20:15 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:35 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-g4mx-q9vg-27p4

2. Revision 2 · amended · 24 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-g4mx-q9vg-27p4

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# Patch Next advisory brief: CVE-2023-45803

Advisory: urllib3's request body not stripped after redirect from 303 status changes request method to GET
IDs: CVE-2023-45803, GHSA-g4mx-q9vg-27p4
Record: https://patchnext.com/advisories/cve-2023-45803 (revision 3, source checked 26 Oct 2026, 13:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: urllib3 2.0.7, 1.26.18. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI urllib3: affected >= 2.0.0, < 2.0.7; < 1.26.18; fixed in 1.26.18, 2.0.7

## 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-g4mx-q9vg-27p4 (OSV record GHSA-g4mx-q9vg-27p4 lists affected ranges: PyPI urllib3 >=2.0.0 =0 <1.26.18 (fixed))
- Verified: https://github.com/advisories/GHSA-g4mx-q9vg-27p4 (GitHub-reviewed advisory GHSA-g4mx-q9vg-27p4 lists affected ranges: PyPI urllib3 >=2.0.0 =0 <1.26.18)

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