urllib3 up to 2.7.x streaming chunk parser HTTPResponse.read_chunked/HTTPResponse.stream chunk-size allocation of resources

Summaryinfo

A vulnerability categorized as problematic has been discovered in urllib3 up to 2.7.x. The impacted element is the function HTTPResponse.read_chunked/HTTPResponse.stream of the component streaming chunk parser. Such manipulation of the argument chunk-size leads to allocation of resources. This vulnerability is referenced as CVE-2026-97689. It is possible to launch the attack remotely. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in urllib3 up to 2.7.x and classified as problematic. Affected by this issue is the function HTTPResponse.read_chunked/HTTPResponse.stream of the component streaming chunk parser. The manipulation of the argument chunk-size with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Impacted is availability. CVE summarizes:

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-97689 since 09/24/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 2.8.0 eliminates this vulnerability.

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Productinfo

Name

• urllib3

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7

Website

• Product: https://github.com/urllib3/urllib3/

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