CVE-2025-61771highCWE-400

CVE-2025-61771: high-severity vulnerability in rack

Rack's multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)

Published

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21Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 7.5epss 0.6%
In short

Rack's form parser loads non-file text fields entirely into memory without limits, allowing attackers to send huge text fields that exhaust server memory and crash the application.

Technical detail

Rack::Multipart::Parser in versions <2.2.19, 3.1.x <3.1.17, and 3.2.x <3.2.2 stores unbounded non-file multipart fields as String objects in memory (CWE-400). An attacker can send multipart/form-data requests with large text fields (hundreds of MB+) to trigger OOM conditions and DoS; impact is amplified under concurrency. Fixed in 2.2.19, 3.1.17, and 3.2.2 with a 2 MiB cap on non-file fields.

Summary generated and translated by AI from the official 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` stores non-file form fields (parts without a `filename`) entirely in memory as Ruby `String` objects. A single large text field in a multipart/form-data request (hundreds of megabytes or more) can consume equivalent process memory, potentially leading to out-of-memory (OOM) conditions and denial of service (DoS). Attackers can send large non-file fields to trigger excessive memory usage. Impact scales with request size and concurrency, potentially leading to worker crashes or severe garbage-collection overhead. All Rack applications processing multipart form submissions are affected. Versions 2.2.19, 3.1.17, and 3.2.2 enforce a reasonable size cap for non-file fields (e.g., 2 MiB). Workarounds include restricting maximum request body size at the web-server or proxy layer (e.g., Nginx `client_max_body_size`) and validating and rejecting unusually large form fields at the application level.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected products
rack · rack
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