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

Moderate severity GitHub Reviewed Published Oct 17, 2023 in urllib3/urllib3 • Updated Nov 6, 2023

Package

pip urllib3 (pip)

Affected versions

>= 2.0.0, < 2.0.7
>= 0, < 1.26.18

Patched versions

2.0.7
1.26.18

Description

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.

References

@sethmlarson sethmlarson published to urllib3/urllib3 Oct 17, 2023
Published by the National Vulnerability Database Oct 17, 2023
Published to the GitHub Advisory Database Oct 17, 2023
Reviewed Oct 17, 2023
Last updated Nov 6, 2023

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Adjacent
Attack complexity
High
Privileges required
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:A/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N

EPSS score

0.043%
(11th percentile)

Weaknesses

CVE ID

CVE-2023-45803

GHSA ID

GHSA-g4mx-q9vg-27p4

Source code

Credits

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