CVE-2026-125109— Rack: Rack::Request#host_with_port (and #base_url / #url) return the raw invalid Host header — incomplete fix of CVE-2026-34835

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 3.0 至 3.1.23 版本以及 3.2.8 版本中，、和方法可能会原样返回由攻击者通过、或头字段控制的无效主机名（authority）。如果应用程序未建立独立的主机白名单，却使用上述方法生成绝对 URL、执行重定向或进行依赖源的检查，则可能输出攻击者指定的分隔符，从而导致重定向被操纵、基于字符串的白名单绕过，或未经转义的标记反射。由于 Rails 已覆写了这些方法，预计不受此问题影响。该问题已在 3.1.23 和 3.2.8 版本中修复。

CVSS 4.8 · Medium Updated Nov 10, 2026

Possible ATT&CK Techniques 2 AI

T1190 · Exploit Public-Facing Application T1566.001 · Spearphishing Attachment

Get alerts for future matching vulnerabilities Log in to subscribe

Vulnerability Information

Have questions about the vulnerability? See if Shenlong's analysis helps!

View Shenlong Deep Dive ↗

Although we use advanced large model technology, its output may still contain inaccurate or outdated information.Shenlong tries to ensure data accuracy, but please verify and judge based on the actual situation.

Vulnerability Title

Rack: Rack::Request#host_with_port (and #base_url / #url) return the raw invalid Host header — incomplete fix of CVE-2026-34835

Source: CVE Program / CVE List V5

Vulnerability Description

Rack is a modular Ruby web server interface. From 3.0 until 3.1.23 and 3.2.8, Rack::Request#host_with_port, #base_url, and #url can return an attacker-controlled invalid authority from Host, X-Forwarded-Host, or Forwarded: host= verbatim. Applications without an independent host allowlist that use these methods for absolute URLs, redirects, or origin-dependent checks can emit attacker-chosen delimiters, enabling redirect manipulation, string-based allowlist bypass, or unescaped markup reflection. Rails overrides these methods and is not expected to be affected. This issue is fixed in versions 3.1.23 and 3.2.8.

Source: CVE Program / CVE List V5

CVSS Information

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

Source: CVE Program / CVE List V5

Vulnerability Type

CWE-1286

Source: CVE Program / CVE List V5

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
rack	rack	>= 3.0, < 3.1.23	-

II. Public POCs for CVE-2026-125109

#	POC Description	Source Link	Shenlong Link

AI-Generated POC Premium

No public POC found.

III. Intelligence Information for CVE-2026-125109

请登录查看更多情报信息。

Other References for CVE-2026-125109 (5)

https://github.com/rack/rack/releases/tag/v3.2.8 x_refsource_MISC
https://github.com/rack/rack/releases/tag/v3.1.23 x_refsource_MISC
https://github.com/rack/rack/security/advisories/GHSA-2j8w-xcrc-x985 x_refsource_CONFIRM
https://github.com/rack/rack/commit/4380381a56dc52556a436d6d794c8e18dc8b0565 x_refsource_MISC
https://github.com/rack/rack/commit/49386f460286b7346c7003b69a839de782cc8a39 x_refsource_MISC

https://www.cve.org/CVERecord?id=CVE-2026-125109

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

CVE-2026-125111	7.5 HIGH	Rack: Multipart parsing allows DoS via unbounded scan buffer growth
CVE-2026-125110	5.3 MEDIUM	Rack: Rack::Static header_rules bypass via dot-segment normalization mismatch
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-1286