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v5.0.30: chore(deps): update dependency urllib3 to v2.6.3 [security]

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v5.0.30
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This PR contains the following updates:

Package Change Age Confidence
urllib3 (changelog) ==2.2.3 → ==2.6.3 age confidence

GitHub Vulnerability Alerts

CVE-2025-50181

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 sethmichaellarson@gmail.com to discuss sponsorship or contribution opportunities.
  • Disable redirects at the request() level instead of the PoolManager() level.

CVE-2025-50182

urllib3 supports being used in a Pyodide runtime utilizing the JavaScript Fetch API or falling back on XMLHttpRequest. This means you can use Python libraries to make HTTP requests from your browser or Node.js. Additionally, urllib3 provides a mechanism to control redirects.

However, the retries and redirect parameters are ignored with Pyodide; the runtime itself determines redirect behavior.

Affected usages

Any code which relies on urllib3 to control the number of redirects for an HTTP request in a Pyodide runtime.

Impact

Redirects are often used to exploit SSRF vulnerabilities. An application attempting to mitigate SSRF or open redirect vulnerabilities by disabling redirects may remain vulnerable if a Pyodide runtime redirect mechanism is unsuitable.

Remediation

If you use urllib3 in Node.js, upgrade to a patched version of urllib3.

Unfortunately, browsers provide no suitable way which urllib3 can use: XMLHttpRequest provides no control over redirects, the Fetch API returns opaqueredirect responses lacking data when redirects are controlled manually. Expect default browser behavior for redirects.

CVE-2025-66418

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.

CVE-2025-66471

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.

CVE-2026-21441

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.

urllib3 can perform decoding or decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). When using the streaming API, the library decompresses only the necessary bytes, enabling partial content consumption.

However, for HTTP redirect responses, the library would read the entire response body to drain the connection and decompress the content unnecessarily. This decompression occurred even before any read methods were called, and configured read limits did not restrict the amount of decompressed data. As a result, there was no safeguard against decompression bombs. A malicious server could exploit this to trigger excessive resource consumption on the client (high CPU usage and large memory allocations for decompressed data; CWE-409).

Affected usages

Applications and libraries using urllib3 version 2.6.2 and earlier to stream content from untrusted sources by setting preload_content=False when they do not disable redirects.

Remediation

Upgrade to at least urllib3 v2.6.3 in which the library does not decode content of redirect responses when preload_content=False.

If upgrading is not immediately possible, disable redirects by setting redirect=False for requests to untrusted source.

Release Notes

urllib3/urllib3 (urllib3)

v2.6.3

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

  • Fixed a high-severity security issue where decompression-bomb safeguards of
    the streaming API were bypassed when HTTP redirects were followed.
    (GHSA-38jv-5279-wg99 <https://github.com/urllib3/urllib3/security/advisories/GHSA-38jv-5279-wg99>__)
  • Started treating Retry-After times greater than 6 hours as 6 hours by
    default. (#&#8203;3743 <https://github.com/urllib3/urllib3/issues/3743>__)
  • Fixed urllib3.connection.VerifiedHTTPSConnection on Emscripten.
    (#&#8203;3752 <https://github.com/urllib3/urllib3/issues/3752>__)

v2.6.2

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

  • Fixed HTTPResponse.read_chunked() to properly handle leftover data in
    the decoder's buffer when reading compressed chunked responses.
    (#&#8203;3734 <https://github.com/urllib3/urllib3/issues/3734>__)

v2.6.1

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

  • Restore previously removed HTTPResponse.getheaders() and
    HTTPResponse.getheader() methods.
    (#&#8203;3731 <https://github.com/urllib3/urllib3/issues/3731>__)

v2.6.0

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

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>__)

v2.5.0

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

Features

  • Added support for the compression.zstd module that is new in Python 3.14.
    See PEP 784 <https://peps.python.org/pep-0784/>_ for more information. (#&#8203;3610 <https://github.com/urllib3/urllib3/issues/3610>__)
  • Added support for version 0.5 of hatch-vcs (#&#8203;3612 <https://github.com/urllib3/urllib3/issues/3612>__)

Bugfixes

  • Fixed a security issue where restricting the maximum number of followed
    redirects at the urllib3.PoolManager level via the retries parameter
    did not work.
  • Made the Node.js runtime respect redirect parameters such as retries
    and redirects.
  • Raised exception for HTTPResponse.shutdown on a connection already released to the pool. (#&#8203;3581 <https://github.com/urllib3/urllib3/issues/3581>__)
  • Fixed incorrect CONNECT statement when using an IPv6 proxy with connection_from_host. Previously would not be wrapped in []. (#&#8203;3615 <https://github.com/urllib3/urllib3/issues/3615>__)

v2.4.0

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

Features

  • Applied PEP 639 by specifying the license fields in pyproject.toml. (#&#8203;3522 <https://github.com/urllib3/urllib3/issues/3522>__)
  • Updated exceptions to save and restore more properties during the pickle/serialization process. (#&#8203;3567 <https://github.com/urllib3/urllib3/issues/3567>__)
  • Added verify_flags option to create_urllib3_context with a default of VERIFY_X509_PARTIAL_CHAIN and VERIFY_X509_STRICT for Python 3.13+. (#&#8203;3571 <https://github.com/urllib3/urllib3/issues/3571>__)

Bugfixes

  • Fixed a bug with partial reads of streaming data in Emscripten. (#&#8203;3555 <https://github.com/urllib3/urllib3/issues/3555>__)

Misc

  • Switched to uv for installing development dependecies. (#&#8203;3550 <https://github.com/urllib3/urllib3/issues/3550>__)
  • Removed the multiple.intoto.jsonl asset from GitHub releases. Attestation of release files since v2.3.0 can be found on PyPI. (#&#8203;3566 <https://github.com/urllib3/urllib3/issues/3566>__)

v2.3.0

Compare Source

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

Features

  • Applied PEP 639 by specifying the license fields in pyproject.toml. (#&#8203;3522 <https://github.com/urllib3/urllib3/issues/3522>__)
  • Updated exceptions to save and restore more properties during the pickle/serialization process. (#&#8203;3567 <https://github.com/urllib3/urllib3/issues/3567>__)
  • Added verify_flags option to create_urllib3_context with a default of VERIFY_X509_PARTIAL_CHAIN and VERIFY_X509_STRICT for Python 3.13+. (#&#8203;3571 <https://github.com/urllib3/urllib3/issues/3571>__)

Bugfixes

  • Fixed a bug with partial reads of streaming data in Emscripten. (#&#8203;3555 <https://github.com/urllib3/urllib3/issues/3555>__)

Misc

  • Switched to uv for installing development dependecies. (#&#8203;3550 <https://github.com/urllib3/urllib3/issues/3550>__)
  • Removed the multiple.intoto.jsonl asset from GitHub releases. Attestation of release files since v2.3.0 can be found on PyPI. (#&#8203;3566 <https://github.com/urllib3/urllib3/issues/3566>__)

Configuration

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