CVE-2026-125111
Rack: Multipart parsing allows DoS via unbounded scan buffer growth
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-400 |
| Vendor | rack |
| Product | rack |
| Published | Nov 9, 2026 |
Stay Ahead of the Next One
Get instant alerts for rack rack
Be the first to know when new high vulnerabilities affecting rack rack are published — delivered to Slack, Telegram or Discord.
Get Free Alerts →
Free · No credit card · 60 sec setup
CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High
Affected Versions
rack / rack
< 2.2.25 >= 3.0, < 3.1.23 >= 3.2, < 3.2.8
References
github.com: https://github.com/rack/rack/security/advisories/GHSA-5v64-555j-wjxm github.com: https://github.com/rack/rack/commit/244e75a840cee0823f86d5d01dc374505a8abed8 github.com: https://github.com/rack/rack/commit/2eaa5b1026a03a43b6537b1a0b233707ba887702 github.com: https://github.com/rack/rack/commit/c9b4698595050838342bd3b5a0fc9ab908065f8f