CVE-2026-125111

What it is

Rack is a modular Ruby web server interface. Prior to 2.2.25, 3.1.23, and 3.2.8, Rack::Multipart::Parser can retain parsed data in its internal StringScanner buffer when reads end inside or immediately after multipart headers. An unauthenticated attacker can align many small parts with rack.multipart.buffer_size boundaries so the buffer grows with the request despite per-field, header, and preamble limits, causing a worker to exhaust memory. The attack requires only a well-formed multipart body and affects applications that parse multipart requests. This issue is fixed in versions 2.2.25, 3.1.23, and 3.2.8.

At a glance

Exploitability

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

Fix

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

Timeline

1. 2026-11-09 17:45 UTC ReservedThe CVE id was reserved by its CNA
2. 2026-11-09 22:02 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2026-11-09 22:02 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: not scored yet.
• Severity: 7.5 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-11-09 22:02 UTC

Last modified

2026-11-09 22:02 UTC

Weakness

CWE-400 · Uncontrolled resource consumption

Record status

Received

Affected

• Rack < 2.2.25
• Rack >= 3.0, < 3.1.23
• Rack >= 3.2, < 3.2.8

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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-125111.md and follow it. Check whether this project is affected by CVE-2026-125111. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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