CVE-2026-125111— Rack: Multipart parsing allows DoS via unbounded scan buffer growth

Quick assessment

Affected

rack rack

Exploitation

No confirmed in-the-wild exploitation; assess based on exposure

Recommended action

Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Rack 是一个模块化的 Ruby Web 服务器接口。在 2.2.25、3.1.23 和 3.2.8 版本之前，当读取操作在 multipart 头部内部或紧接其后结束时，Rack::Multipart::Parser 会将其解析后的数据保留在内部的 StringScanner 缓冲区中。未认证的攻击者可以通过将大量小型部分与 rack.multipart.buffer_size 边界对齐，使得缓冲区在请求过程中持续增长，即使存在针对字段、头部和前言的单独限制，最终导致工作进程耗尽内存。该攻击仅需构造一个格式正确

CVSS 7.5 · High Updated Nov 10, 2026

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

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Vulnerability Information

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Vulnerability Title

Rack: Multipart parsing allows DoS via unbounded scan buffer growth

Source: CVE Program / CVE List V5

Vulnerability Description

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.

Source: CVE Program / CVE List V5

CVSS Information

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Source: CVE Program / CVE List V5

Vulnerability Type

未加控制的资源消耗(资源穷尽)

Source: CVE Program / CVE List V5

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
rack	rack	< 2.2.25	-

II. Public POCs for CVE-2026-125111

#	POC Description	Source Link	Shenlong Link

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III. Intelligence Information for CVE-2026-125111

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Other References for CVE-2026-125111 (4)

https://github.com/rack/rack/security/advisories/GHSA-5v64-555j-wjxm x_refsource_CONFIRM
https://github.com/rack/rack/commit/244e75a840cee0823f86d5d01dc374505a8abed8 x_refsource_MISC
https://github.com/rack/rack/commit/c9b4698595050838342bd3b5a0fc9ab908065f8f x_refsource_MISC
https://github.com/rack/rack/commit/2eaa5b1026a03a43b6537b1a0b233707ba887702 x_refsource_MISC

https://www.cve.org/CVERecord?id=CVE-2026-125111

Same Patch Batch · rack · 2026-11-09 · 4 CVEs total

CVE-2026-125110	5.3 MEDIUM	Rack: Rack::Static header_rules bypass via dot-segment normalization mismatch
CVE-2026-125109	4.8 MEDIUM	Rack: Rack::Request#host_with_port (and #base_url / #url) return the raw invalid Host head
CVE-2026-125108	3.7 LOW	Rack: Multipart boundary ambiguity guard in Rack::Multipart::Parser can be bypassed with a

IV. Related Vulnerabilities

Same product: rack

Same vendor: rack

Same weakness: CWE-400