Sourced from urllib3's releases.

2.6.3

🚀 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. (urllib3/urllib3#3743)
• Fixed urllib3.connection.VerifiedHTTPSConnection on Emscripten. (urllib3/urllib3#3752)

2.6.2

🚀 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.

Changes

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

2.6.1

🚀 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)

2.6.0

🚀 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. 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.

... (truncated)

Sourced from urllib3's changelog.

2.6.3 (2026-01-07)

• 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. ([#3743](https://github.com/urllib3/urllib3/issues/3743) <https://github.com/urllib3/urllib3/issues/3743>__)
• Fixed urllib3.connection.VerifiedHTTPSConnection on Emscripten. ([#3752](https://github.com/urllib3/urllib3/issues/3752) <https://github.com/urllib3/urllib3/issues/3752>__)

2.6.2 (2025-12-11)

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

2.6.1 (2025-12-08)

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

2.6.0 (2025-12-05)

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

... (truncated)

• 0248277 Release 2.6.3
• 8864ac4 Merge commit from fork
• 70cecb2 Fix Scorecard issues related to vulnerable dev dependencies (#3755)
• 41f249a Move "v2.0 Migration Guide" to the end of the table of contents (#3747)
• fd4dffd Patch VerifiedHTTPSConnection for Emscripten (#3752)
• 13f0bfd Handle massive values in Retry-After when calculating time to sleep for (#3743)
• 8c480bf Bump actions/upload-artifact from 5.0.0 to 6.0.0 (#3748)
• 4b40616 Bump actions/cache from 4.3.0 to 5.0.1 (#3750)
• 82b8479 Bump actions/download-artifact from 6.0.0 to 7.0.0 (#3749)
• 34284cb Mention experimental features in the security policy (#3746)
• Additional commits viewable in compare view