The Cybersecurity and Infrastructure Security Agency (CISA) has issued a critical warning about an actively exploited path traversal vulnerability in the Ruby on Rails framework. Tracked as CVE-2019-5418, this flaw allows attackers to access arbitrary files on target servers. Given the active exploitation, CISA has added this vulnerability to its Known Exploited Vulnerabilities (KEV) catalog and set a remediation deadline of July 28, 2025. This blog post provides an overview of the vulnerability, its potential impact, and the necessary steps to mitigate the risk.

Vulnerability Details

CVE-2019-5418, is a path traversal flaw that affects the Action View component of Ruby on Rails. It falls under the Common Weakness Enumeration category CWE-22, which includes weaknesses that allow attackers to access files and directories stored outside the intended directory structure.

Attackers can exploit this vulnerability by crafting malicious HTTP Accept headers and calls to render file: functions. This allows them to navigate outside the application’s intended file scope and access sensitive system files.

An example of a malicious request is:

GET /vulnerable_endpoint HTTP/1.1
Host: victim.com
Accept: ../../../../etc/passwd

In vulnerable Rails code, the unsafe pattern looks like this:

# Vulnerable usage
render file: params[:file]

If params[:file] If it is not sanitized correctly, an attacker can supply a value like ../../../../etc/passwd, causing Rails to render and disclose the contents of /etc/passwd or other sensitive files.

Impact & Exploit Potential

Successful exploitation of CVE-2019-5418 can lead to arbitrary file disclosure, allowing unauthorized access to sensitive server files. This includes:

• Configuration files
• Database credentials
• Source code
• Other sensitive information

Relevant techniques and tactics include:

 T1190 – Exploit Public-Facing Application: The severity of the vulnerability is amplified because it can expose confidential data, facilitating further attacks or system compromise.

TA0006 – Credential Access can be achieved by exploiting this vulnerability.

Affected Products

The vulnerability affects the following versions of the Ruby on Rails framework:

• Ruby on Rails framework (Action View component) versions before Rails 4.2.5.1
• Ruby on Rails framework (Action View component) versions before Rails 5.1.6.2

Mitigation Strategies

CISA mandates that federal agencies and organizations apply vendor-provided mitigations immediately. The primary mitigation involves:

• Updating Rails to patched versions: Rails 4.2.5.1, Rails 5.1.6.2, or later versions that address this vulnerability.
• Implement strict input validation for file rendering operations and avoid using render file: user-controlled parameters.
• Implement proper access controls and conduct thorough code reviews to identify vulnerable patterns.
• Deploying Web Application Firewalls (WAF) configured to detect and block path traversal attempts.

Organizations must also ensure that applications follow the principle of least privilege, restricting file system access to only necessary directories and implementing comprehensive logging to detect potential exploitation attempts.

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