CVE-2025-61771

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

0.6% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2025-10-07 15:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-19 16:10 UTC Last updatedMost recent change to the record

Details

Published

2025-10-07 15:16 UTC

Last modified

2026-10-19 16:10 UTC

Exploit probability

0.6% · EPSS, next 30 days

Weakness

CWE-400 · Uncontrolled resource consumption

Record status

Analyzed

Affected

• Rack < 2.2.19
• Rack < 3.1.17
• Rack < 3.2.2

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High