Update dependency urllib3 to v2.6.0 [SECURITY] (1.3) - autoclosed

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
urllib3 (changelog)	2.5.0 -> 2.6.0
urllib3 (changelog)	>=1.26.17 -> >=2.6.0

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urllib3 allows an unbounded number of links in the decompression chain

CVE-2025-66418 / GHSA-gm62-xv2j-4w53

More information

Details

Impact

urllib3 supports chained HTTP encoding algorithms for response content according to RFC 9110 (e.g., Content-Encoding: gzip, zstd).

However, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data.

Affected usages

Applications and libraries using urllib3 version 2.5.0 and earlier for HTTP requests to untrusted sources unless they disable content decoding explicitly.

Remediation

Upgrade to at least urllib3 v2.6.0 in which the library limits the number of links to 5.

If upgrading is not immediately possible, use preload_content=False and ensure that resp.headers["content-encoding"] contains a safe number of encodings before reading the response content.

Severity

• CVSS Score: 8.9 / 10 (High)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

References

• https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53
• https://nvd.nist.gov/vuln/detail/CVE-2025-66418
• https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8
• https://github.com/urllib3/urllib3

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

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urllib3 streaming API improperly handles highly compressed data

CVE-2025-66471 / GHSA-2xpw-w6gg-jr37

More information

Details

Impact

urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once.

When streaming a compressed response, urllib3 can perform decoding or decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). The library must read compressed data from the network and decompress it until the requested chunk size is met. Any resulting decompressed data that exceeds the requested amount is held in an internal buffer for the next read operation.

The decompression logic could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This can result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data; CWE-409) on the client side, even if the application only requested a small chunk of data.

Affected usages

Applications and libraries using urllib3 version 2.5.0 and earlier to stream large compressed responses or content from untrusted sources.

stream(), read(amt=256), read1(amt=256), read_chunked(amt=256), readinto(b) are examples of urllib3.HTTPResponse method calls using the affected logic unless decoding is disabled explicitly.

Remediation

Upgrade to at least urllib3 v2.6.0 in which the library avoids decompressing data that exceeds the requested amount.

If your environment contains a package facilitating the Brotli encoding, upgrade to at least Brotli 1.2.0 or brotlicffi 1.2.0.0 too. These versions are enforced by the urllib3[brotli] extra in the patched versions of urllib3.

Credits

The issue was reported by @​Cycloctane.
Supplemental information was provided by @​stamparm during a security audit performed by 7ASecurity and facilitated by OSTIF.

Severity

• CVSS Score: 8.9 / 10 (High)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

References

• https://github.com/urllib3/urllib3/security/advisories/GHSA-2xpw-w6gg-jr37
• https://nvd.nist.gov/vuln/detail/CVE-2025-66471
• https://github.com/urllib3/urllib3/commit/c19571de34c47de3a766541b041637ba5f716ed7
• https://github.com/urllib3/urllib3

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

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

CVE-2023-45803 / GHSA-g4mx-q9vg-27p4 / PYSEC-2023-212

More information

Details

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.

Severity

• CVSS Score: 5.7 / 10 (Medium)
• Vector String: 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

References

• https://github.com/urllib3/urllib3/security/advisories/GHSA-g4mx-q9vg-27p4
• https://nvd.nist.gov/vuln/detail/CVE-2023-45803
• https://github.com/urllib3/urllib3/commit/4e50fbc5db74e32cabd5ccc1ab81fc103adfe0b3
• https://github.com/urllib3/urllib3/commit/4e98d57809dacab1cbe625fddeec1a290c478ea9
• 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/[email protected]/message/4R2Y5XK3WALSR3FNAGN7JBYV2B343ZKB
• https://lists.fedoraproject.org/archives/list/[email protected]/message/5F5CUBAN5XMEBVBZPHFITBLMJV5FIJJ5
• https://lists.fedoraproject.org/archives/list/[email protected]/message/PPDPLM6UUMN55ESPQWJFLLIZY4ZKCNRX
• https://www.rfc-editor.org/rfc/rfc9110.html#name-get

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

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CVE-2023-45803 / GHSA-g4mx-q9vg-27p4 / PYSEC-2023-212

More information

Details

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.

Severity

• CVSS Score: 4.2 / 10 (Medium)
• Vector String: CVSS:3.1/AV:A/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N

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/[email protected]/message/PPDPLM6UUMN55ESPQWJFLLIZY4ZKCNRX/

This data is provided by OSV and the PyPI Advisory Database (CC-BY 4.0).

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urllib3's Proxy-Authorization request header isn't stripped during cross-origin redirects

CVE-2024-37891 / GHSA-34jh-p97f-mpxf

More information

Details

When using urllib3's proxy support with ProxyManager, the Proxy-Authorization header is only sent to the configured proxy, as expected.

However, when sending HTTP requests without using urllib3's proxy support, it's possible to accidentally configure the Proxy-Authorization header even though it won't have any effect as the request is not using a forwarding proxy or a tunneling proxy. In those cases, urllib3 doesn't treat the Proxy-Authorization HTTP header as one carrying authentication material and thus doesn't strip the header on cross-origin redirects.

Because this is a highly unlikely scenario, we believe the severity of this vulnerability is low for almost all users. Out of an abundance of caution urllib3 will automatically strip the Proxy-Authorization header during cross-origin redirects to avoid the small chance that users are doing this on accident.

Users should use urllib3's proxy support or disable automatic redirects to achieve safe processing of the Proxy-Authorization header, but we still 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:

• Setting the Proxy-Authorization header without using urllib3's built-in proxy support.
• Not disabling HTTP redirects.
• Either not using an HTTPS origin server or for the proxy or target origin to redirect to a malicious origin.

Remediation

• Using the Proxy-Authorization header with urllib3's ProxyManager.
• Disabling HTTP redirects using redirects=False when sending requests.
• Not using the Proxy-Authorization header.

Severity

• CVSS Score: 4.4 / 10 (Medium)
• Vector String: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N

References

• https://github.com/urllib3/urllib3/security/advisories/GHSA-34jh-p97f-mpxf
• https://nvd.nist.gov/vuln/detail/CVE-2024-37891
• https://github.com/urllib3/urllib3/commit/40b6d1605814dd1db0a46e202d6e56f2e4c9a468
• https://github.com/urllib3/urllib3/commit/accff72ecc2f6cf5a76d9570198a93ac7c90270e
• https://github.com/urllib3/urllib3
• https://lists.debian.org/debian-lts-announce/2024/12/msg00020.html
• https://security.netapp.com/advisory/ntap-20240822-0003
• https://www.vicarius.io/vsociety/posts/proxy-authorization-header-handling-vulnerability-in-urllib3-cve-2024-37891

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

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urllib3 redirects are not disabled when retries are disabled on PoolManager instantiation

CVE-2025-50181 / GHSA-pq67-6m6q-mj2v

More information

Details

urllib3 handles redirects and retries using the same mechanism, which is controlled by the Retry object. The most common way to disable redirects is at the request level, as follows:

resp = urllib3.request("GET", "https://httpbin.org/redirect/1", redirect=False)
print(resp.status)

##### 302

However, it is also possible to disable redirects, for all requests, by instantiating a PoolManager and specifying retries in a way that disable redirects:

import urllib3

http = urllib3.PoolManager(retries=0)  # should raise MaxRetryError on redirect
http = urllib3.PoolManager(retries=urllib3.Retry(redirect=0))  # equivalent to the above
http = urllib3.PoolManager(retries=False)  # should return the first response

resp = http.request("GET", "https://httpbin.org/redirect/1")

However, the retries parameter is currently ignored, which means all the above examples don't disable redirects.

Affected usages

Passing retries on PoolManager instantiation to disable redirects or restrict their number.

By default, requests and botocore users are not affected.

Impact

Redirects are often used to exploit SSRF vulnerabilities. An application attempting to mitigate SSRF or open redirect vulnerabilities by disabling redirects at the PoolManager level will remain vulnerable.

Remediation

You can remediate this vulnerability with the following steps:

• Upgrade to a patched version of urllib3. If your organization would benefit from the continued support of urllib3 1.x, please contact [email protected] to discuss sponsorship or contribution opportunities.
• Disable redirects at the request() level instead of the PoolManager() level.

Severity

• CVSS Score: 5.3 / 10 (Medium)
• Vector String: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

References

• https://github.com/urllib3/urllib3/security/advisories/GHSA-pq67-6m6q-mj2v
• https://nvd.nist.gov/vuln/detail/CVE-2025-50181
• https://github.com/urllib3/urllib3/commit/f05b1329126d5be6de501f9d1e3e36738bc08857
• https://github.com/urllib3/urllib3

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

Release Notes

urllib3/urllib3 (urllib3)

v2.6.0

Compare Source

==================

Security

• Fixed a security issue where streaming API could improperly handle highly
  compressed HTTP content ("decompression bombs") leading to excessive resource
  consumption even when a small amount of data was requested. Reading small
  chunks of compressed data is safer and much more efficient now.
  (GHSA-2xpw-w6gg-jr37 <https://github.com/urllib3/urllib3/security/advisories/GHSA-2xpw-w6gg-jr37>__)
• Fixed a security issue where an attacker could compose an HTTP response with
  virtually unlimited links in the Content-Encoding header, potentially
  leading to a denial of service (DoS) attack by exhausting system resources
  during decoding. The number of allowed chained encodings is now limited to 5.
  (GHSA-gm62-xv2j-4w53 <https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53>__)

.. caution::

• If urllib3 is not installed with the optional urllib3[brotli] extra, but
  your environment contains a Brotli/brotlicffi/brotlipy package anyway, make
  sure to upgrade it to at least Brotli 1.2.0 or brotlicffi 1.2.0.0 to
  benefit from the security fixes and avoid warnings. Prefer using
  urllib3[brotli] to install a compatible Brotli package automatically.

• If you use custom decompressors, please make sure to update them to
  respect the changed API of urllib3.response.ContentDecoder.

Features

• Enabled retrieval, deletion, and membership testing in HTTPHeaderDict using bytes keys. (#&#8203;3653 <https://github.com/urllib3/urllib3/issues/3653>__)
• Added host and port information to string representations of HTTPConnection. (#&#8203;3666 <https://github.com/urllib3/urllib3/issues/3666>__)
• Added support for Python 3.14 free-threading builds explicitly. (#&#8203;3696 <https://github.com/urllib3/urllib3/issues/3696>__)

Removals

• Removed the HTTPResponse.getheaders() method in favor of HTTPResponse.headers.
  Removed the HTTPResponse.getheader(name, default) method in favor of HTTPResponse.headers.get(name, default). (#&#8203;3622 <https://github.com/urllib3/urllib3/issues/3622>__)

Bugfixes

• Fixed redirect handling in urllib3.PoolManager when an integer is passed
  for the retries parameter. (#&#8203;3649 <https://github.com/urllib3/urllib3/issues/3649>__)
• Fixed HTTPConnectionPool when used in Emscripten with no explicit port. (#&#8203;3664 <https://github.com/urllib3/urllib3/issues/3664>__)
• Fixed handling of SSLKEYLOGFILE with expandable variables. (#&#8203;3700 <https://github.com/urllib3/urllib3/issues/3700>__)

Misc

• Changed the zstd extra to install backports.zstd instead of zstandard on Python 3.13 and before. (#&#8203;3693 <https://github.com/urllib3/urllib3/issues/3693>__)
• Improved the performance of content decoding by optimizing BytesQueueBuffer class. (#&#8203;3710 <https://github.com/urllib3/urllib3/issues/3710>__)
• Allowed building the urllib3 package with newer setuptools-scm v9.x. (#&#8203;3652 <https://github.com/urllib3/urllib3/issues/3652>__)
• Ensured successful urllib3 builds by setting Hatchling requirement to >= 1.27.0. (#&#8203;3638 <https://github.com/urllib3/urllib3/issues/3638>__)

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