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.
Metrics
Affected Vendors & Products
References
History
Tue, 07 Oct 2025 16:15:00 +0000
Type | Values Removed | Values Added |
---|---|---|
Metrics |
ssvc
|
Tue, 07 Oct 2025 14:45:00 +0000
Type | Values Removed | Values Added |
---|---|---|
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. | |
Title | Rack's unbounded multipart preamble buffering enables DoS (memory exhaustion) | |
Weaknesses | CWE-400 | |
References |
| |
Metrics |
cvssV3_1
|

Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2025-10-07T15:43:06.827Z
Reserved: 2025-09-30T19:43:49.900Z
Link: CVE-2025-61770

Updated: 2025-10-07T15:35:12.484Z

Status : Received
Published: 2025-10-07T15:16:02.950
Modified: 2025-10-07T15:16:02.950
Link: CVE-2025-61770

No data.

No data.