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Message-ID: <fe6ae308-dd2d-441a-8afa-3d9742274aa1@oracle.com>
Date: Fri, 5 Dec 2025 10:52:54 -0800
From: Alan Coopersmith <alan.coopersmith@...cle.com>
To: oss-security@...ts.openwall.com
Subject: CVE-2025-66418 & CVE-2025-66471 fixed in urllib3 2.6.0
https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53
discloses:
> Unbounded number of links in the decompression chain
> ====================================================
>
> illia-v published GHSA-gm62-xv2j-4w53 Dec 5, 2025
>
> Package: urllib3 (pip)
> Affected versions: >=1.24,<2.6.0
> Patched versions: 2.6.0
>
> Description
> ===========
>
> Impact
> ------
>
> urllib3 supports chained HTTP encoding algorithms for response content
> according to RFC 9110 (e.g., Content-Encoding: gzip, zstd).
>
> However, the number of links in the decompression chain was unbounded
> allowing a malicious server to insert a virtually unlimited number of
> compression steps leading to high CPU usage and massive memory
> allocation for the decompressed data.
>
> Affected usages
> ---------------
>
> Applications and libraries using urllib3 version 2.5.0 and earlier for
> HTTP requests to untrusted sources unless they disable content
> decoding explicitly.
>
> Remediation
> -----------
>
> Upgrade to at least urllib3 v2.6.0 in which the library limits the
> number of links to 5.
>
> If upgrading is not immediately possible, use preload_content=False
> and ensure that resp.headers["content-encoding"] contains a safe
> number of encodings before reading the response content.
>
> Severity: High 8.9 / 10
> CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
> CVE ID: CVE-2025-66418
> Weaknesses: Weakness CWE-770
>
> Credits
> -------
> @illia-v illia-v Reporter
> @sethmlarson sethmlarson Remediation reviewer
> @pquentin pquentin Remediation reviewer
https://github.com/urllib3/urllib3/security/advisories/GHSA-2xpw-w6gg-jr37
advises:
> Streaming API improperly handles highly compressed data
> =======================================================
>
> illia-v published GHSA-2xpw-w6gg-jr37 Dec 5, 2025
>
> Package: urllib3 (pip)
> Affected versions: >=1.0,<2.6.0
> Patched versions: 2.6.0
>
> Description
> ===========
>
> Impact
> ------
>
> 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.
>
> When streaming a compressed response, urllib3 can perform decoding or
> decompression based on the HTTP Content-Encoding header (e.g., gzip,
> deflate, br, or zstd). The library must read compressed data from the
> network and decompress it until the requested chunk size is met. Any
> resulting decompressed data that exceeds the requested amount is held
> in an internal buffer for the next read operation.
>
> The decompression logic could cause urllib3 to fully decode a small
> amount of highly compressed data in a single operation. This can
> result in excessive resource consumption (high CPU usage and massive
> memory allocation for the decompressed data; CWE-409) on the client
> side, even if the application only requested a small chunk of data.
>
> Affected usages
> ---------------
>
> Applications and libraries using urllib3 version 2.5.0 and earlier to
> stream large compressed responses or content from untrusted sources.
>
> stream(), read(amt=256), read1(amt=256), read_chunked(amt=256),
> readinto(b) are examples of urllib3.HTTPResponse method calls using
> the affected logic unless decoding is disabled explicitly.
>
> Remediation
> -----------
>
> Upgrade to at least urllib3 v2.6.0 in which the library avoids
> decompressing data that exceeds the requested amount.
>
> If your environment contains a package facilitating the Brotli
> encoding, upgrade to at least Brotli 1.2.0 or brotlicffi 1.2.0.0
> too. These versions are enforced by the urllib3[brotli] extra in the
> patched versions of urllib3.
>
> Credits
> -------
>
> The issue was reported by @Cycloctane.
>
> Supplemental information was provided by @stamparm during a security
> audit performed by 7ASecurity and facilitated by OSTIF.
>
> Severity: High 8.9 / 10
> CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
> CVE ID: CVE-2025-66471
> Weaknesses: Weakness CWE-409
>
> Credits
> -------
>
> @illia-v illia-v Coordinator
> @pquentin pquentin Remediation reviewer
> @sethmlarson sethmlarson Analyst
> @Cycloctane Cycloctane Finder
> @stamparm stamparm Finder
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