CVE-2026-9375
Decompression Bomb Bypass via Negative max_length in Streaming API in urllib3
Description
urllib3 version 2.6.3 is vulnerable to a decompression bomb bypass in its streaming API (`preload_content=False`) when using Brotli support. The issue arises due to three independent code paths in `response.py` that bypass the `max_length` protection introduced in version 2.6.0 to mitigate CVE-2025-66471. Specifically, negative `max_length` values can be produced due to buffer arithmetic in `read()`, `flush_decoder` unconditionally overrides `max_length` to `-1`, and `_flush_decoder()` passes no limit at all, defaulting to unlimited decompression. This allows a malicious HTTP server to trigger an out-of-memory (OOM) condition by decompressing large payloads into memory, leading to a denial of service (DoS). The vulnerability affects urllib3 2.6.3 and Brotli 1.2.0 and impacts applications and libraries using `requests` or `urllib3` to stream content from untrusted sources.
INFO
Published Date :
June 19, 2026, 6:45 p.m.
Last Modified :
June 19, 2026, 6:45 p.m.
Remotely Exploit :
No
Source :
@huntr_ai
Affected Products
The following products are affected by CVE-2026-9375
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
Solution
- Update urllib3 to the latest version.
- Update Brotli to the latest version.
- Ensure max_length protection is enforced.
- Avoid streaming untrusted content.
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