Rack’s unbounded multipart preamble buffering enables DoS (memory exhaustion)

7.5 / 10

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Description

Rack is a modular Ruby web server interface. In versions prior to 2.2.19, 3.1.17, and 3.2.2, `Rack::Multipart::Parser` buffers the entire multipart preamble (bytes before the first boundary) in memory without any size limit. A client can send a large preamble followed by a valid boundary, causing significant memory use and potential process termination due to out-of-memory (OOM) conditions. Remote attackers can trigger large transient memory spikes by including a long preamble in multipart/form-data requests. The impact scales with allowed request sizes and concurrency, potentially causing worker crashes or severe slowdown due to garbage collection. Versions 2.2.19, 3.1.17, and 3.2.2 enforce a preamble size limit (e.g., 16 KiB) or discard preamble data entirely. Workarounds include limiting total request body size at the proxy or web server level and monitoring memory and set per-process limits to prevent OOM conditions.

Basic Information

ID CVE-2025-61770

Source GitHub_M

Published Oct 7, 2025 at 14:30

Modified Oct 7, 2025 at 14:42

Affected Product

Vendor rack

Product rack

Version < 2.2.19

Affected Versions rack rack < 2.2.19
rack rack >= 3.1, < 3.1.17
rack rack >= 3.2, < 3.2.2

CWE Classification

CWE-400

References

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    "published": "2025-10-07T14:30:04.552Z",
    "modified": "2025-10-07T14:42:04.268Z",
    "type": "cve",
    "title": "Rack's unbounded multipart preamble buffering enables DoS (memory exhaustion)",
    "source": "GitHub_M",
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Rack’s unbounded multipart preamble buffering enables DoS (memory exhaustion)_CVE-2025-61770