Details

Impact

When following cross-origin redirects for requests made using urllib3’s high-level APIs, such as urllib3.request(), PoolManager.request(), and ProxyManager.request(), sensitive headers — Authorization, Cookie, and Proxy-Authorization (defined in Retry.DEFAULT_REMOVE_HEADERS_ON_REDIRECT) — are stripped by default, as expected.

However, cross-origin redirects followed from the low-level API via ProxyManager.connection_from_url().urlopen(..., assert_same_host=False) still forward these sensitive headers.

Affected usage

Applications and libraries using urllib3 versions earlier than 2.7.0 may be affected if they allow cross-origin redirects while making requests through HTTPConnection.urlopen() instances created via ProxyManager.connection_from_url().

Remediation

Upgrade to urllib3 version 2.7.0 or later, in which sensitive headers are stripped from redirects followed by HTTPConnection.

If upgrading is not immediately possible, avoid using this low-level redirect flow for cross-origin redirects. If appropriate for your use case, switch to ProxyManager.request().

Severity

• CVSS Score: 8.2 / 10 (High)
• Vector String: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

References

• https://github.com/urllib3/urllib3/security/advisories/GHSA-qccp-gfcp-xxvc
• https://github.com/advisories/GHSA-qccp-gfcp-xxvc

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

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.

urllib3 can perform decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). When using the streaming API since version 2.6.0, the library decompresses only the necessary bytes, enabling partial content consumption.

However, urllib3 before version 2.7.0 could still decompress the whole response instead of the requested portion in two cases:

1. During the second HTTPResponse.read(amt=N) call when the response was decompressed using the official Brotli library.
2. When HTTPResponse.drain_conn() was called after the response had been read and decompressed partially (compression algorithm did not matter here).

These issues could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This could result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data; CWE-409) on the client side.

Affected usages

Applications and libraries using urllib3 versions earlier than 2.7.0 may be affected when streaming compressed responses from untrusted sources in either of these cases, unless decompression is explicitly disabled:

1. A response encoded with br is read incrementally with at least two HTTPResponse.read(amt=N) or HTTPResponse.stream(amt=N) calls while using the official Brotli library.
2. HTTPResponse.drain_conn() is called after response decompression has already started.

Remediation

Upgrade to at least urllib3 version 2.7.0 in which the library:

1. Is more efficient for reads with Brotli.
2. Always skips decompression for HTTPResponse.drain_conn().

If upgrading is not immediately possible, the following workarounds may reduce exposure in specific cases:

1. For the Brotli-specific issue only, switch from brotli to brotlicffi until you can upgrade urllib3; the official Brotli package is affected because of https://github.com/google/brotli/issues/1396.
2. If your code explicitly calls HTTPResponse.drain_conn(), call HTTPResponse.close() instead when connection reuse is not important.

Credits

The Brotli-specific issue was reported by @​kimkou2024.
HTTPResponse.drain_conn() inefficiency was reported by @​Cycloctane.

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-mf9v-mfxr-j63j
• https://github.com/advisories/GHSA-mf9v-mfxr-j63j

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

v2.7.0

Compare Source

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

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.
  2. During the second HTTPResponse.read(amt=N) or
     HTTPResponse.stream(amt=N) call when the response was decompressed
     using the official Brotli <https://pypi.org/project/brotli/>__ library.

  See GHSA-mf9v-mfxr-j63j <https://github.com/urllib3/urllib3/security/advisories/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 <https://github.com/urllib3/urllib3/security/advisories/GHSA-qccp-gfcp-xxvc>__)

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.
  (#&#8203;3763 <https://github.com/urllib3/urllib3/issues/3763>__)
• Removed support for end-of-life Python 3.9.
  (#&#8203;3720 <https://github.com/urllib3/urllib3/issues/3720>__)
• Removed support for end-of-life PyPy3.10.
  (#&#8203;4979 <https://github.com/urllib3/urllib3/issues/4979>__)
• Bumped the minimum supported pyOpenSSL version to 19.0.0.
  (#&#8203;3777 <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.
  (#&#8203;3636 <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.
  (#&#8203;4967 <https://github.com/urllib3/urllib3/issues/4967>__)
• Fixed HTTPResponse.stream() and HTTPResponse.read_chunked() to handle
  amt=0.
  (#&#8203;3793 <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.
  (#&#8203;3798 <https://github.com/urllib3/urllib3/issues/3798>__)
• Fixed LocationParseError when paths resembling schemeless URIs were
  passed to HTTPConnectionPool.urlopen().
  (#&#8203;3352 <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.
  (#&#8203;3764 <https://github.com/urllib3/urllib3/issues/3764>__)