CVE-2026-125109
Description
A flaw was found in Rack. A remote attacker can exploit this vulnerability by sending HTTP requests with specially crafted host headers containing invalid characters. Because the interface returns unvalidated host data when authority validation fails, applications relying on it to construct URLs may be manipulated into redirecting users to malicious destinations, bypassing security allowlists, or reflecting unescaped content.
Statement
This vulnerability is rated as Moderate severity because successful exploitation requires an application to consume unvalidated authority helpers directly without host restrictions, restricting the blast radius to header-driven URL manipulation or redirection tampering. Standard frameworks such as Ruby on Rails override these helper routines with custom implementations and remain unaffected by default. Furthermore, deployments positioned behind reverse proxies that sanitize or overwrite forwarded routing headers prevent external manipulation of the request authority.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 4.8 | N/A | 4.8 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | Low | N/A | Low |
| Integrity Impact | Low | N/A | Low |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
Understanding the Weakness (CWE)
Other
Technical Impact: Varies by Context
When untrusted input is not properly validated for the expected syntax, attackers could cause parsing failures, trigger unexpected errors, or expose latent vulnerabilities that might not be directly exploitable if the input had conformed to the syntax.
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