urllib3's request body not stripped after redirect from 303 status changes request method to GET
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, many users aren't putting sensitive data in HTTP request bodies, if this is the case then this vulnerability isn't exploitable.
Both of the following conditions must be true to be affected by this vulnerability:
- If you're using urllib3 and submitting sensitive information in the HTTP request body (such as form data or JSON)
- The origin service is compromised and starts redirecting using 303 to a malicious peer or the redirected-to service becomes compromised.
Remediation
You can remediate this vulnerability with any of the following steps:
- Upgrade to a patched version of urllib3 (v1.26.18 or v2.0.7)
- Disable redirects for services that you aren't expecting to respond with redirects with
redirects=False. - Disable automatic redirects with
redirects=Falseand handle 303 redirects manually by stripping the HTTP request body.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | urllib3 | >= 2.0.0, < 2.0.7, < 1.26.18 | 2.0.7, 1.26.18 |
References
- https://github.com/urllib3/urllib3/security/advisories/GHSA-g4mx-q9vg-27p4
- https://www.rfc-editor.org/rfc/rfc9110.html#name-get
- https://github.com/urllib3/urllib3/commit/4e98d57809dacab1cbe625fddeec1a290c478ea9
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PPDPLM6UUMN55ESPQWJFLLIZY4ZKCNRX/
- https://nvd.nist.gov/vuln/detail/CVE-2023-45803
- https://github.com/urllib3/urllib3/commit/4e50fbc5db74e32cabd5ccc1ab81fc103adfe0b3
- https://github.com/urllib3/urllib3/commit/b594c5ceaca38e1ac215f916538fb128e3526a36
- https://github.com/pypa/advisory-database/tree/main/vulns/urllib3/PYSEC-2023-212.yaml
- https://github.com/urllib3/urllib3
- https://github.com/urllib3/urllib3/releases/tag/1.26.18
- https://github.com/urllib3/urllib3/releases/tag/2.0.7
- https://lists.debian.org/debian-lts-announce/2024/12/msg00020.html
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4R2Y5XK3WALSR3FNAGN7JBYV2B343ZKB
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/5F5CUBAN5XMEBVBZPHFITBLMJV5FIJJ5
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PPDPLM6UUMN55ESPQWJFLLIZY4ZKCNRX
- CVSS vector
CVSS:3.1/AV:A/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N- Weakness (CWE)
CWE-200- Platform
- Python (PyPI)
- Package
urllib3- Disclosed
- 17.10.2023
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2023-212 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-g4mx-q9vg-27p4 - 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 request body not stripped after redirect from 303 status changes request method to GET 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.