urllib3 up to 2.6.x on Python HTTPResponse.drain_conn data amplification

Summaryinfo

A vulnerability marked as problematic has been reported in urllib3 up to 2.6.x on Python. The affected element is the function HTTPResponse.drain_conn. Performing a manipulation results in data amplification. This vulnerability was named CVE-2026-44432. The attack may be initiated remotely. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in urllib3 up to 2.6.x on Python. It has been classified as problematic. This affects the function HTTPResponse.drain_conn. The manipulation with an unknown input leads to a data amplification vulnerability. CWE is classifying the issue as CWE-409. The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output. This is going to have an impact on availability. The summary by CVE is:

urllib3 is an HTTP client library for Python. From 2.6.0 to before 2.7.0, urllib3 could decompress the whole response instead of the requested portion (1) during the second HTTPResponse.read(amt=N) call when the response was decompressed using the official Brotli library or (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) on the client side. This vulnerability is fixed in 2.7.0.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-44432 since 05/06/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 2.7.0 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• urllib3

Version

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

Website

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

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion