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CVE-2026-9375— Decompression Bomb Bypass via Negative max_length in Streaming API in urllib3

AI Predicted 6.5 Difficulty: Easy

Possible ATT&CK Techniques 1AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProductVersion RangeStatus
urllib3urllib3/urllib3unspecified< 2.7.0affected
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I. Basic Information for CVE-2026-9375

Vulnerability Information
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Vulnerability Title
Decompression Bomb Bypass via Negative max_length in Streaming API in urllib3
Source: NVD (National Vulnerability Database)
Vulnerability 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.
Source: NVD (National Vulnerability Database)
CVSS Information
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: NVD (National Vulnerability Database)

Affected Products

VendorProductAffected VersionsCPESubscribe
urllib3urllib3/urllib3 unspecified ~ 2.7.0 -

II. Public POCs for CVE-2026-9375

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III. Intelligence Information for CVE-2026-9375

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Patches & Fixes for CVE-2026-9375 (1)

Vendor Advisories for CVE-2026-9375 (1)

IV. Related Vulnerabilities

Same vendor: urllib3
Same weakness: CWE-400

V. Comments for CVE-2026-9375

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