GHSA-v845-jxx5-vc9f CVE-2023-43804 PYSEC-2023-192

`Cookie` HTTP header isn't stripped on cross-origin redirects

High PyPI

Severity: 7.4 / 10; High · CVSS 4.0
Exploit chance (EPSS): 1.36%; Chance of exploitation in the next 30 days. Higher than 71.74% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
Fix: 2.0.6; Upgrade urllib3 to this version or later

Description

urllib3 doesn't treat the Cookie HTTP header special or provide any helpers for managing cookies over HTTP, that is the responsibility of the user. However, it is possible for a user to specify a Cookie header and unknowingly leak information via HTTP redirects to a different origin if that user doesn't disable redirects explicitly.

Users must handle redirects themselves instead of relying on urllib3's automatic redirects to achieve safe processing of the Cookie header, thus we decided to strip the header by default in order to further protect users who aren't using the correct approach.

Affected usages

We believe the number of usages affected by this advisory is low. It requires all of the following to be true to be exploited:

Using an affected version of urllib3 (patched in v1.26.17 and v2.0.6)
Using the Cookie header on requests, which is mostly typical for impersonating a browser.
Not disabling HTTP redirects
Either not using HTTPS or for the origin server to redirect to a malicious origin.

Remediation

Upgrading to at least urllib3 v1.26.17 or v2.0.6
Disabling HTTP redirects using redirects=False when sending requests.
Not using the Cookie header.

Affected versions

PyPI

Package	Vulnerable	Fixed in
urllib3	`>= 2.0.0, < 2.0.6`	`2.0.6`
urllib3	`< 1.26.17`	`1.26.17`
urllib3	`>= 2.0.0, < 2.0.6`	`2.0.6`
urllib3	`< 1.26.17`	`1.26.17`
urllib3	`>= 2.0.0, < 2.0.6` `< 1.26.17`	`1.26.17` `2.0.6`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

urllib3 PyPI → `2.0.6`

pip

pip install --upgrade "urllib3>=2.0.6"

poetry

poetry add "urllib3>=2.0.6"

uv

uv add "urllib3>=2.0.6"

Severity breakdown

CVSS 4.0 7.4

CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: Low
Attack requirements: Present
Privileges required: High
User interaction: None
Confidentiality (vulnerable system): High
Integrity (vulnerable system): High
Availability (vulnerable system): None
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

CVSS 3.1 5.9

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:N

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

Weakness

CWE-200: Exposure of Sensitive Information to an Unauthorized Actor

The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.

How to prevent it

Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

References

Advisories

Fixes and patches

Packages

github.com/urllib3/urllib3

Timeline

Oct 2, 2023 Published
Sep 10, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-vxq7-64xx-v4gw urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory	High	Also affects urllib3
GHSA-gh4c-6fx4-qh6g urllib3: Chunked Deflate streaming can enter an infinite loop	Medium	Also affects urllib3
GHSA-8988-9cw3-xx77 urllib3: HTTPS proxy TLS configuration may be ignored or overridden	High	Also affects urllib3
GHSA-mf9v-mfxr-j63j urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API	High	Also affects urllib3
GHSA-qccp-gfcp-xxvc urllib3: Sensitive headers forwarded across origins in proxied low-level redirects	High	Also affects urllib3
GHSA-38jv-5279-wg99 Decompression-bomb safeguards bypassed when following HTTP redirects (streaming API)	High	Also affects urllib3
GHSA-2xpw-w6gg-jr37 urllib3 streaming API improperly handles highly compressed data	High	Also affects urllib3
GHSA-gm62-xv2j-4w53 urllib3 allows an unbounded number of links in the decompression chain	High	Also affects urllib3

Credits: illia-v, pquentin, ranjit-git, sethmlarson

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