CVE-2026-125109

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

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 22:18 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2026-11-10 17:17 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: 4.8 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-11-09 22:18 UTC

Last modified

2026-11-10 17:17 UTC

Weakness

CWE-1286

Record status

Received

Attack profile CVSS 3.1 · 4.8

Attack vector

Network

Complexity

High

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None

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-2026-125109.md and follow it. Check whether this project is affected by CVE-2026-125109. 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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