CVE-2026-97688

urllib3 is an HTTP client library for Python. From 2.6.2 until 2.8.0, HTTPResponse.stream and HTTPResponse.read_chunked can enter an infinite loop because the Deflate decoder retains trailing bytes as unconsumed input after reaching end-of-stream and repeatedly decodes them without progress. The issue occurs when an untrusted server sends a chunked Deflate response whose decoded body exceeds a positive finite chunk size and whose encoded body has trailing bytes, specifically a response with Transfer-Encoding: chunked and Content-Encoding: deflate, content decoding enabled, and the positive finite amt=N streaming chunk size. The attack mechanism is that a malicious server returns a compressed chunked response with trailing bytes after the Deflate stream. The impact is excessive CPU usage and a request that does not complete, and network read timeouts do not interrupt the loop because no further socket read occurs. This issue is fixed in version 2.8.0.

Impact

urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading content in chunks instead of loading the entire response body into memory at once.

urllib3 can decompress response bodies according to the HTTP Content-Encoding header. When streaming a compressed, chunked response, urllib3 first consumes data already buffered by the decoder before reading the next HTTP chunk.

However, urllib3 versions from 2.6.2 through 2.7.0 could enter an infinite loop when a chunked response contained bytes after the end of the Deflate stream. If the decompressed body exceeded the requested streaming chunk size, Python's zlib implementation could retain the trailing bytes as unconsumed input after reaching the end of the compressed stream. urllib3 would repeatedly attempt to decode those same bytes without making progress or reading more data from the network.

A malicious server could exploit this behavior to cause excessive CPU usage and prevent the affected request from completing on the client. Network read timeouts would not interrupt the loop because no further socket operation was required.

Affected usages

Applications and libraries using urllib3 versions 2.6.2 through 2.7.0 may be affected when all of the following conditions are met:

1. Compressed responses from an untrusted source are streamed using HTTPResponse.stream(amt=N) or HTTPResponse.read_chunked(amt=N) with a positive, finite chunk size.
2. Content decoding is enabled.
3. The response uses both Transfer-Encoding: chunked and Content-Encoding: deflate.
4. The decoded body exceeds the requested chunk size and the encoded body contains bytes after the end of the Deflate stream.

HTTPResponse.stream() uses a finite chunk size by default and is therefore affected when the other conditions are met.

Remediation

Upgrade to urllib3 2.8.0, in which the Deflate decoder stops accepting input after reaching the end of the compressed stream and no longer reports trailing bytes as data that can produce more decoded output.

If upgrading is not immediately possible, disable automatic content decoding for responses from untrusted sources by setting decode_content=False, or reject streamed responses using the Deflate content encoding. Applications that disable automatic decoding must handle the compressed response safely at another layer.

Impact

urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading content in chunks instead of loading the entire response body into memory at once.

urllib3 can decompress response bodies according to the HTTP Content-Encoding header. When streaming a compressed, chunked response, urllib3 first consumes data already buffered by the decoder before reading the next HTTP chunk.

However, urllib3 versions from 2.6.2 through 2.7.0 could enter an infinite loop when a chunked response contained bytes after the end of the Deflate stream. If the decompressed body exceeded the requested streaming chunk size, Python's zlib implementation could retain the trailing bytes as unconsumed input after reaching the end of the compressed stream. urllib3 would repeatedly attempt to decode those same bytes without making progress or reading more data from the network.

A malicious server could exploit this behavior to cause excessive CPU usage and prevent the affected request from completing on the client. Network read timeouts would not interrupt the loop because no further socket operation was required.

Affected usages

Applications and libraries using urllib3 versions 2.6.2 through 2.7.0 may be affected when all of the following conditions are met:

1. Compressed responses from an untrusted source are streamed using HTTPResponse.stream(amt=N) or HTTPResponse.read_chunked(amt=N) with a positive, finite chunk size.
2. Content decoding is enabled.
3. The response uses both Transfer-Encoding: chunked and Content-Encoding: deflate.
4. The decoded body exceeds the requested chunk size and the encoded body contains bytes after the end of the Deflate stream.

HTTPResponse.stream() uses a finite chunk size by default and is therefore affected when the other conditions are met.

Remediation

Upgrade to urllib3 2.8.0, in which the Deflate decoder stops accepting input after reaching the end of the compressed stream and no longer reports trailing bytes as data that can produce more decoded output.

If upgrading is not immediately possible, disable automatic content decoding for responses from untrusted sources by setting decode_content=False, or reject streamed responses using the Deflate content encoding. Applications that disable automatic decoding must handle the compressed response safely at another layer.

urllib3 is an HTTP client library for Python. From 2.6.2 until 2.8.0, HTTPResponse.stream and HTTPResponse.read_chunked can enter an infinite loop because the Deflate decoder retains trailing bytes as unconsumed input after reaching end-of-stream and repeatedly decodes them without progress. The issue occurs when an untrusted server sends a chunked Deflate response whose decoded body exceeds a positive finite chunk size and whose encoded body has trailing bytes, specifically a response with Transfer-Encoding: chunked and Content-Encoding: deflate, content decoding enabled, and the positive finite amt=N streaming chunk size. The attack mechanism is that a malicious server returns a compressed chunked response with trailing bytes after the Deflate stream. The impact is excessive CPU usage and a request that does not complete, and network read timeouts do not interrupt the loop because no further socket read occurs. This issue is fixed in version 2.8.0.

These are all security issues fixed in the python313-urllib3-2.8.0-1.1 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the python313-urllib3_1-1.26.20-8.1 package on the GA media of openSUSE Tumbleweed.

This update for python-urllib3 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

This update for python-urllib3_1 fixes the following issues:

• CVE-2026-97687: traffic interception due to possible HTTPS proxy TLS configuration override (bsc#1283908).
• CVE-2026-97688: denial of service due to infinite loop during chunked Deflate decoding (bsc#1283909).
• CVE-2026-97689: denial of service due to unbounded memory allocation in chunk parser (bsc#1283910).

Yu-Fu Fu, Seth Larson and Yonatan Magier discovered that urllib3 did not correctly handle certain certificate validations. An attacker could possibly use this issue to observe or modify forwarded traffic. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-97687)

Martin Desrumaux discovered that urllib3 did not correctly handle decoding certain deflate responses. An attacker could possibly use this issue to cause a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-97688)

It was discovered that urllib3 did not correctly handle certain memory operations. An attacker could possibly use this issue to cause a denial of service. (CVE-2026-97689)