What changed in urllib3 from 1 to 2

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

Security

Addressed high-severity security issues. Impact was limited to specific use cases detailed in the accompanying advisories; overall user exposure was estimated to be marginal.

• Decompression-bomb safeguards of the streaming API were bypassed:

  1. When HTTPResponse.drain_conn() was called after the response had been read and decompressed partially. (Reported by @Cycloctane)
  2. During the second HTTPResponse.read(amt=N) or HTTPResponse.stream(amt=N) call when the response was decompressed using the official Brotli library. (Reported by @kimkou2024)

  See GHSA-mf9v-mfxr-j63j for details.

• HTTP pools created using ProxyManager.connection_from_url did not strip sensitive headers specified in Retry.remove_headers_on_redirect when redirecting to a different host. (GHSA-qccp-gfcp-xxvc reported by @christos-spearbit)

Deprecations and Removals

• Used FutureWarning instead of DeprecationWarning for better visibility of existing deprecation notices. Rescheduled the removal of deprecated features to version 3.0. (https://github.com/urllib3/urllib3/issues/3763)
• Removed support for end-of-life Python 3.9. (https://github.com/urllib3/urllib3/issues/3720)
• Removed support for end-of-life PyPy3.10. (https://github.com/urllib3/urllib3/issues/4979)
• Bumped the minimum supported pyOpenSSL version to 19.0.0. (https://github.com/urllib3/urllib3/issues/3777)

Bugfixes

• Fixed a bug where HTTPResponse.read(amt=None) was ignoring decompressed data buffered from previous partial reads. (https://github.com/urllib3/urllib3/issues/3636)
• Fixed a bug where HTTPResponse.read() could cache only part of the response after a partial read when cache_content=True. (https://github.com/urllib3/urllib3/issues/4967)
• Fixed HTTPResponse.stream() and HTTPResponse.read_chunked() to handle amt=0. (https://github.com/urllib3/urllib3/issues/3793)
• Updated _TYPE_BODY type alias to include missing Iterable[str], matching the documented and runtime behavior of chunked request bodies. (https://github.com/urllib3/urllib3/issues/3798)
• Fixed LocationParseError when paths resembling schemeless URIs were passed to HTTPConnectionPool.urlopen(). (https://github.com/urllib3/urllib3/issues/3352)
• Fixed BaseHTTPResponse.readinto() type annotation to accept memoryview in addition to bytearray, matching the io.RawIOBase.readinto contract and enabling use with io.BufferedReader without type errors. (https://github.com/urllib3/urllib3/issues/3764)

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

Changes

• Fixed a security issue where decompression-bomb safeguards of the streaming API were bypassed when HTTP redirects were followed. (CVE-2026-21441 reported by @D47A, 8.9 High, GHSA-38jv-5279-wg99)
• Started treating Retry-After times greater than 6 hours as 6 hours by default. (https://github.com/urllib3/urllib3/issues/3743)
• Fixed urllib3.connection.VerifiedHTTPSConnection on Emscripten. (https://github.com/urllib3/urllib3/issues/3752)

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

Changes

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

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

Changes

• Restore previously removed HTTPResponse.getheaders() and HTTPResponse.getheader() methods. (#3731)

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

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. (CVE-2025-66471 reported by @Cycloctane, 8.9 High, 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. (CVE-2025-66418 reported by @illia-v, 8.9 High, GHSA-gm62-xv2j-4w53)

[!IMPORTANT]

• 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. (#3653)
• Added host and port information to string representations of HTTPConnection. (#3666)
• Added support for Python 3.14 free-threading builds explicitly. (#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). (#3622)

Bugfixes

• Fixed redirect handling in urllib3.PoolManager when an integer is passed for the retries parameter. (#3649)
• Fixed HTTPConnectionPool when used in Emscripten with no explicit port. (#3664)
• Fixed handling of SSLKEYLOGFILE with expandable variables. (#3700)

Misc

• Changed the zstd extra to install backports.zstd instead of zstandard on Python 3.13 and before. (#3693)
• Improved the performance of content decoding by optimizing BytesQueueBuffer class. (#3710)
• Allowed building the urllib3 package with newer setuptools-scm v9.x. (#3652)
• Ensured successful urllib3 builds by setting Hatchling requirement to ≥ 1.27.0. (#3638)

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

Security issues

urllib3 2.5.0 fixes two moderate security issues:

• Pool managers now properly control redirects when retries is passed — CVE-2025-50181 reported by @sandumjacob (5.3 Medium, GHSA-pq67-6m6q-mj2v)
• Redirects are now controlled by urllib3 in the Node.js runtime — CVE-2025-50182 (5.3 Medium, GHSA-48p4-8xcf-vxj5)

Features

• Added support for the compression.zstd module that is new in Python 3.14. See PEP 784 for more information. (#3610)
• Added support for version 0.5 of hatch-vcs (#3612)

Bugfixes

• Raised exception for HTTPResponse.shutdown on a connection already released to the pool. (#3581)
• Fixed incorrect CONNECT statement when using an IPv6 proxy with connection_from_host. Previously would not be wrapped in []. (#3615)

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

Features

• Applied PEP 639 by specifying the license fields in pyproject.toml. (#3522)
• Updated exceptions to save and restore more properties during the pickle/serialization process. (#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+. (#3571)

Bugfixes

• Fixed a bug with partial reads of streaming data in Emscripten. (#3555)

Misc

• Switched to uv for installing development dependecies. (#3550)
• Removed the multiple.intoto.jsonl asset from GitHub releases. Attestation of release files since v2.3.0 can be found on PyPI. (#3566)

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support for 2023. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

Features

• Added HTTPResponse.shutdown() to stop any ongoing or future reads for a specific response. It calls shutdown(SHUT_RD) on the underlying socket. This feature was sponsored by LaunchDarkly. (https://github.com/urllib3/urllib3/issues/2868)
• Added support for JavaScript Promise Integration on Emscripten. This enables more efficient WebAssembly requests and streaming, and makes it possible to use in Node.js if you launch it as node --experimental-wasm-stack-switching. (https://github.com/urllib3/urllib3/issues/3400)
• Added the proxy_is_tunneling property to HTTPConnection and HTTPSConnection. (https://github.com/urllib3/urllib3/issues/3285)
• Added pickling support to NewConnectionError and NameResolutionError. (https://github.com/urllib3/urllib3/issues/3480)

Bugfixes

• Fixed an issue in debug logs where the HTTP version was rendering as "HTTP/11" instead of "HTTP/1.1". (https://github.com/urllib3/urllib3/issues/3489)

Deprecations and Removals

• Removed support for Python 3.8. (https://github.com/urllib3/urllib3/issues/3492)

Full Changelog: https://github.com/urllib3/urllib3/compare/2.2.3...2.3.0

🚀 urllib3 is fundraising for HTTP/2 support

urllib3 is raising ~$40,000 USD to release HTTP/2 support and ensure long-term sustainable maintenance of the project after a sharp decline in financial support for 2023. If your company or organization uses Python and would benefit from HTTP/2 support in Requests, pip, cloud SDKs, and thousands of other projects please consider contributing financially to ensure HTTP/2 support is developed sustainably and maintained for the long-haul.

Thank you for your support.

Features

• Added support for Python 3.13. (#3473)

Bugfixes

• Fixed the default encoding of chunked request bodies to be UTF-8 instead of ISO-8859-1. All other methods of supplying a request body already use UTF-8 starting in urllib3 v2.0. (#3053)
• Fixed ResourceWarning on CONNECT with Python < 3.11.4 by backporting https://github.com/python/cpython/issues/103472. (`#3252)
• Adjust tolerance for floating-point comparison on Windows to avoid flakiness in CI (#3413)
• Fixed a crash where certain standard library hash functions were absent in restricted environments. (#3432)
• Fixed mypy error when adding to HTTPConnection.default_socket_options. (#3448)

HTTP/2 (experimental)

HTTP/2 support is still in early development.

• Excluded Transfer-Encoding: chunked from HTTP/2 request body (#3425)
• Added version checking for h2 (https://pypi.org/project/h2/) usage. Now only accepting supported h2 major version 4.x.x. (#3290)
• Added a probing mechanism for determining whether a given target origin supports HTTP/2 via ALPN. (#3301)
• Add support for sending a request body with HTTP/2 (#3302)

Full Changelog: https://github.com/urllib3/urllib3/compare/2.2.2...2.2.3