CVE-2026-9375

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector : AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/urllib3/urllib3/commit/2bdcc44d1e163fb5cc48a8662425e35e15adfe6a
https://huntr.com/bounties/ddd09eb9-b87d-4a43-84df-48837b1bbc23
https://huntr.com/bounties/ddd09eb9-b87d-4a43-84df-48837b1bbc23

Configurations

No configuration.

History

22 Jun 2026, 18:16

Type	Values Removed	Values Added
References	~~() https://huntr.com/bounties/ddd09eb9-b87d-4a43-84df-48837b1bbc23 -~~	() https://huntr.com/bounties/ddd09eb9-b87d-4a43-84df-48837b1bbc23 -

19 Jun 2026, 19:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-06-19 19:16

Updated : 2026-06-22 19:49

NVD link : CVE-2026-9375

Mitre link : CVE-2026-9375

CVE.ORG link : CVE-2026-9375

JSON object : View

Products Affected

No product.

CWE

CWE-400

Uncontrolled Resource Consumption

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