CVE-2015-1840 in Ruby on Rails
Summary
by MITRE
jquery_ujs.js in jquery-rails before 3.1.3 and 4.x before 4.0.4 and rails.js in jquery-ujs before 1.0.4, as used with Ruby on Rails 3.x and 4.x, allow remote attackers to bypass the Same Origin Policy, and trigger transmission of a CSRF token to a different-domain web server, via a leading space character in a URL within an attribute value.
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Analysis
by VulDB Data Team • 01/14/2026
The vulnerability described in CVE-2015-1840 represents a critical security flaw in the jquery-rails and jquery-ujs libraries that affected Ruby on Rails applications running version 3.x and 4.x. This issue stems from improper handling of URL parsing within the javascript libraries that facilitate cross-site request forgery protection mechanisms. The vulnerability specifically targets the Same Origin Policy enforcement which is fundamental to web security, creating a pathway for attackers to bypass essential protection measures that prevent unauthorized requests from being executed on behalf of authenticated users.
The technical flaw manifests through a subtle but exploitable parsing behavior where a leading space character in URL attributes within javascript code causes the browser to interpret the URL differently than intended. When jquery_ujs.js or rails.js processes form attributes containing such malformed URLs, the space character creates a parsing ambiguity that allows the CSRF token to be transmitted to a malicious third-party domain instead of the intended target server. This occurs because the javascript libraries fail to properly sanitize or validate URL attributes before constructing the request, enabling attackers to manipulate the target of token transmission through carefully crafted input.
The operational impact of this vulnerability is significant as it effectively neutralizes the CSRF protection mechanisms that are integral to Ruby on Rails applications. Attackers can leverage this flaw to perform cross-site request forgery attacks by tricking users into visiting malicious websites that contain specially crafted forms or links. When users with active sessions on legitimate Rails applications visit these malicious sites, the vulnerable javascript libraries will transmit the user's CSRF token to the attacker-controlled domain, enabling the attacker to perform authenticated actions on behalf of the user. This creates a pathway for unauthorized transactions, data modification, or account takeovers depending on the application's functionality.
This vulnerability maps to CWE-346: "Origin Validation Error" and CWE-352: "Cross-Site Request Forgery (CSRF)" within the Common Weakness Enumeration framework, demonstrating how improper input validation can lead to fundamental security policy violations. From the MITRE ATT&CK framework perspective, this represents a technique for bypassing security controls and can be categorized under T1071.004: "Application Layer Protocol: DNS" and T1566: "Phishing" as part of a broader attack chain that includes social engineering to deliver malicious payloads. The vulnerability also aligns with T1212: "Exploitation for Credential Access" as it enables unauthorized access to user sessions through token theft.
Mitigation strategies for this vulnerability require immediate updates to the affected jquery-rails and jquery-ujs libraries to versions 3.1.3, 4.0.4, or 1.0.4 respectively, which contain the necessary fixes for proper URL parsing and validation. Organizations should also implement comprehensive input sanitization measures at the application level, particularly for form attributes and URL parameters that are processed by javascript libraries. Additionally, network-level monitoring should be enhanced to detect unusual patterns of token transmission to external domains, and security teams should conduct thorough code reviews to identify other potential parsing vulnerabilities in javascript libraries. The fix implemented in the updated versions ensures that URL attributes are properly validated and sanitized before being processed, thereby restoring the intended Same Origin Policy enforcement and preventing the unauthorized transmission of CSRF tokens to third-party domains.