CVE-2023-45803: Request body not stripped after redirect in urllib3
A flaw found in the urllib3. The urllib3 is a user-friendly HTTP client library for Python. urllib3 previously wouldn't remove the HTTP request body when an HTTP redirect response using status 301, 302, or 303 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 this behavior 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. 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: 1. Using urllib3 and submitting sensitive information in the HTTP request body (such as form data or JSON) and 2. The origin service is compromised and starts redirecting using 301, 302, or 303 to a malicious peer or the redirected-to service becomes compromised. This issue has been addressed in versions 1.26.18 and 2.0.7 and users are advised to update to resolve this issue. Users unable to update should disable redirects for services that aren't expecting to respond with redirects with redirects=False and disable automatic redirects with redirects=False and handle 301, 302, and 303 redirects manually by stripping the HTTP request body.
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
Other sources
Request body not stripped after redirect in urllib3
— Microsoft
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=False and handle 303 redirects manually by stripping the HTTP request body.
— GitHub
Affected Software
Remediation
Event History
Frequently Asked Questions
What is CVE-2023-45803?
CVE-2023-45803 is a vulnerability in urllib3 that allows an HTTP request body to remain after a method change to `GET` in a redirect response.
What is the severity of CVE-2023-45803?
The severity of CVE-2023-45803 is medium with a CVSS score of 4.2.
How does CVE-2023-45803 affect the urllib3 package?
CVE-2023-45803 affects urllib3 package versions 1.26.17 and earlier and versions 2.0.0 to 2.0.6. It has been fixed in version 1.26.18 and 2.0.7.
How can I fix CVE-2023-45803?
To fix CVE-2023-45803, update the urllib3 package to version 1.26.18 or 2.0.7 using pip.
Where can I find more information about CVE-2023-45803?
More information about CVE-2023-45803 can be found in the advisory and commits on the urllib3 GitHub repository: - Advisory: [here](https://github.com/urllib3/urllib3/security/advisories/GHSA-g4mx-q9vg-27p4) - Commit 1: [here](https://github.com/urllib3/urllib3/commit/4e50fbc5db74e32cabd5ccc1ab81fc103adfe0b3) - Commit 2: [here](https://github.com/urllib3/urllib3/commit/b594c5ceaca38e1ac215f916538fb128e3526a36)