CVE-2025-27221 identifies a security flaw in the Ruby URI gem prior to version 1.0.3, specifically in the handling of Uniform Resource Identifiers (URIs). The vulnerability arises because the URI handling methods—URI.join, URI#merge, and URI#+—do not properly remove the userinfo component (which contains authentication credentials such as username and password) when the host portion of the URI is changed. This results in the inadvertent retention and potential leakage of sensitive authentication credentials during URI manipulation. The flaw is categorized under CWE-212, which refers to the improper removal of sensitive information before storage or transfer. The vulnerability has a CVSS v3.1 base score of 3.2, indicating low severity due to factors such as local attack vector (AV:L), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), and limited confidentiality impact (C:L). There are no known exploits in the wild, and the issue primarily threatens confidentiality without affecting integrity or availability. The affected versions include 0, 0.12.0, 0.13.0, and 1.0.0 of the URI gem. The root cause is that when URI methods modify the host, they fail to clear the userinfo field, which can lead to sensitive credentials being unintentionally propagated or exposed in logs, error messages, or downstream systems. This can be particularly problematic in web applications or services that dynamically construct or manipulate URIs for API calls, redirects, or resource access. The recommended remediation is to upgrade to URI gem version 1.0.3 or later, where this issue has been fixed. Additionally, developers should audit their codebases for unsafe URI manipulations that might retain sensitive information and implement secure coding practices to avoid credential leakage.

For European organizations, the primary impact of CVE-2025-27221 is the potential leakage of authentication credentials embedded in URIs during manipulation. This can lead to unauthorized disclosure of sensitive information, which may facilitate further attacks such as unauthorized access or credential theft. Although the vulnerability does not directly compromise system integrity or availability, the confidentiality breach could undermine trust, lead to compliance violations (e.g., GDPR), and expose organizations to reputational damage. Organizations relying on Ruby-based web applications, APIs, or microservices that use the affected URI gem versions are at risk, especially if they handle sensitive user credentials or internal authentication tokens within URIs. The low CVSS score and lack of known exploits suggest a limited immediate threat, but the risk increases if attackers discover ways to exploit this leakage in complex attack chains. European sectors with stringent data protection requirements, such as finance, healthcare, and government, should prioritize addressing this vulnerability to maintain compliance and secure sensitive data flows.

1. Upgrade the Ruby URI gem to version 1.0.3 or later immediately to ensure the vulnerability is patched. 2. Conduct a thorough code review focusing on all instances where URIs are constructed or manipulated using URI.join, URI#merge, or URI#+, verifying that userinfo components are not unintentionally retained or exposed. 3. Implement logging and monitoring to detect any unusual URI patterns or potential credential leakage in application logs or network traffic. 4. Avoid embedding sensitive credentials directly in URIs; use alternative secure authentication mechanisms such as headers or tokens. 5. Educate developers on secure URI handling practices and the risks of retaining sensitive information in URI components. 6. For legacy systems where immediate upgrade is not feasible, consider applying code-level patches or wrappers that explicitly clear userinfo fields after URI manipulations. 7. Review and update security policies to include checks for sensitive data leakage in URI handling during development and security assessments.