CVE-2026-44432

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.

Credits

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

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.

CVE-2026-44432 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.7.0); upgrading removes the vulnerable code path.

Kodem intelligence

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.

1. What is CVE-2026-44432? CVE-2026-44432 is a high-severity security vulnerability in urllib3 (pip), affecting versions >= 2.6.0, < 2.7.0. It is fixed in 2.7.0.
2. How severe is CVE-2026-44432? CVE-2026-44432 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of urllib3 are affected by CVE-2026-44432? urllib3 (pip) versions >= 2.6.0, < 2.7.0 is affected.
4. Is there a fix for CVE-2026-44432? Yes. CVE-2026-44432 is fixed in 2.7.0. Upgrade to this version or later.
5. Is CVE-2026-44432 exploitable, and should I be worried? Whether CVE-2026-44432 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-44432 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-44432? Upgrade urllib3 to 2.7.0 or later.