🚀 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. 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 the following security issues:

• The TLS configuration for HTTPS proxies could be ignored or overridden. (High severity, GHSA-8988-9cw3-xx77)
• HTTPResponse.stream() and read_chunked() could buffer a chunk-size line of unbounded length in memory. (High severity, GHSA-vxq7-64xx-v4gw)
• Chunked Deflate streaming could enter an infinite loop. (Medium severity, GHSA-gh4c-6fx4-qh6g)

Deprecations & Removals

• Deprecated using an empty collection as the Retry option allowed_methods to retry any verb. (#5044)

Features

• Added Url.auth_decoded and Url.auth_decoded_joined convenience properties to the result of parse_url(). (#4945)
• Added basic_auth_encoding and proxy_basic_auth_encoding parameters to urllib3.util.make_headers(). (#5092)

Bugfixes

• Fixed response header handling to replace obsolete folded header lines (obs-fold) with spaces in accordance with RFC 9112, preventing raw CRLF sequences from appearing in header values such as Set-Cookie. (#1362)

• Fixed usage of proxy_ssl_context with ProxyManager when use_forwarding_for_https=True. Passing ssl_context instead of proxy_ssl_context for HTTPS proxies in this configuration now emits a FutureWarning and will raise an error in v3.0. (#2577)

• Changed behavior of the default ConnectionPool.pool initialization. LifoQueue is now resolved from the queue module after the ConnectionPool is instantiated instead of using the default cached QueueCls class property. This is done because sometimes the queue.LifoQueue is monkey-patched late in the program, such as by gevent. (#3289)

• Raised UnrewindableBodyError instead of ValueError when retrying a request whose body had tell() but not seek(). (#3779)

• Decoded percent-encoded SOCKS proxy credentials before authenticating with the proxy server. (#3785)

• Fixed HTTPResponse.drain_conn() to discard unread response data in 64 KiB chunks (same as the default amt when doing HTTPResponse.stream(...)). (#5019)

• Fixed is_ipaddress() to detect non-standard IPv4 forms accepted by socket.connect, such as hex (0x7f000001), octal (0177.0.0.1), and decimal integers (2130706433), ensuring SSL certificate verification uses the correct mode for these addresses. (#5029)

• Fixed HTTPConnectionPool.urlopen raising a misleading FullPoolError instead of ValueError when called with an invalid timeout argument on a pool created with block=True. (#5059)

• Fixed port-zero handling to preserve explicit :0 values instead of substituting the default ports 80 or 443 in URL parsing, pool selection, proxy configuration, connection_from_url(), and HTTP/2 request authority. (#5071, #5101)

• Fixed a bug where PoolManager passed the assert_hostname and assert_fingerprint parameters to HTTP connection pools. (#5077)

• Fixed HTTPConnectionPool.urlopen() and HTTP proxy forwarding to strip URL fragments from absolute request targets before sending requests. (#5079)

• Added safeguards to the proxy tunneling code to prevent potential security issues when handling invalid characters in the proxy host and HTTP headers. This change affects users of Python 3.10, Python 3.11, and Python 3.12 when the standard library does not contain the fix; those on newer Python versions should upgrade to 3.13.14+ or 3.14.5+ to get the same security fixes. (#5091)

• Fixed HTTPSConnection.connect() overriding ProxyConfig.ssl_context's certificate policy and proxy identity checks with the target connection's TLS settings when forwarding through an HTTPS proxy.

  HTTPSConnection no longer applies target SNI, assertions, or client credentials to forwarding proxy handshakes and continues to use its ssl_context as a fallback when an HTTPS proxy forwards an HTTP target. (#5093)

• Fixed URL parsing to more strictly enforce RFC 3986 host syntax, rejecting invalid host input such as raw spaces and control characters, malformed percent-encodings, and percent-encoded control characters in HTTP(S) hosts and IPv6 zone identifiers, including proxy CONNECT tunnel targets. Host normalization now also follows RFC 3986 normalization rules for percent-encoded octets by decoding percent-encoded unreserved characters and uppercasing the hexadecimal digits of retained percent-encoded octets. (#5095)

• Fixed an AttributeError on Python built with OpenSSL 4+, where ssl.PROTOCOL_TLSv1 no longer exists. (#5097)

• Fixed urllib3.contrib.pyopenssl to use cryptography APIs when reading a certificate subject and loading encrypted private keys, avoiding DeprecationWarning raised by pyOpenSSL 26.3.0+. (#5103)

• Fixed handling of HTTP 303 redirects for requests with chunked or file-like bodies. (#5161)

• Fixed assert_fingerprint() to raise SSLError instead of binascii.Error when a fingerprint has a supported length but contains non-hexadecimal characters. (#5211)

Misc

• Added a test dependency group containing the minimum dependencies needed to run the test suite, intended for downstream packagers. The dev-base and mypy groups now include this new group via include-group, removing duplication. (#3594)
• Fixed test failures with pytest >= 9.1. (#5094)
• Enabled JSPI tests with Firefox in the Emscripten test suite. (#5166)
• Improved streamed response decoding performance. (#5209)
• Fixed flaky tests. (#5232, #5234, #5239)

🚀 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. (#3763)
• Removed support for end-of-life Python 3.9. (#3720)
• Removed support for end-of-life PyPy3.10. (#4979)
• Bumped the minimum supported pyOpenSSL version to 19.0.0. (#3777)

Bugfixes

• Fixed a bug where HTTPResponse.read(amt=None) was ignoring decompressed data buffered from previous partial reads. (#3636)
• Fixed a bug where HTTPResponse.read() could cache only part of the response after a partial read when cache_content=True. (#4967)
• Fixed HTTPResponse.stream() and HTTPResponse.read_chunked() to handle amt=0. (#3793)
• Updated _TYPE_BODY type alias to include missing Iterable[str], matching the documented and runtime behavior of chunked request bodies. (#3798)
• Fixed LocationParseError when paths resembling schemeless URIs were passed to HTTPConnectionPool.urlopen(). (#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. (#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. (#3743)
• Fixed urllib3.connection.VerifiedHTTPSConnection on Emscripten. (#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. (#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)

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. (#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. (#3400)
• Added the proxy_is_tunneling property to HTTPConnection and HTTPSConnection. (#3285)
• Added pickling support to NewConnectionError and NameResolutionError. (#3480)

Bugfixes

• Fixed an issue in debug logs where the HTTP version was rendering as "HTTP/11" instead of "HTTP/1.1". (#3489)

Deprecations and Removals

• Removed support for Python 3.8. (#3492)

Full Changelog: 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 python/cpython#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: 2.2.2...2.2.3