Resource exhaustion in Rack
CVE-2026-125111
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.
Vulnerability class: DoS (Denial of Service)
Published .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Rack — versions < 2.2.25, >= 3.0, < 3.1.23, >= 3.2, < 3.2.8
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-125111?
- CVE-2026-125111 is a high-severity vulnerability in Rack, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-11-09.
- How severe is CVE-2026-125111?
- High severity. CVSS v3 base score is 7.5 out of 10.