CVE-2009-4924 in python-cjson
Summary
by MITRE
Dan Pascu python-cjson 1.0.5 does not properly handle a [ / ] argument to cjson.encode, which makes it easier for remote attackers to conduct certain cross-site scripting (XSS) attacks involving Firefox and the end tag of a SCRIPT element.
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Analysis
by VulDB Data Team • 02/06/2019
The vulnerability identified as CVE-2009-4924 affects the python-cjson library version 1.0.5, specifically targeting the cjson.encode function's handling of forward slash characters within input data. This flaw represents a cross-site scripting vulnerability that exploits how the library processes special characters during JSON encoding operations. The issue arises from improper sanitization of input parameters, particularly when a forward slash character is included as part of the argument passed to the encode function, creating potential injection points for malicious script execution.
The technical implementation of this vulnerability stems from the library's inadequate handling of the forward slash character in its encoding logic. When the cjson.encode function processes input containing a forward slash, it fails to properly escape or sanitize this character according to JSON standards, potentially allowing attackers to inject malicious content. This flaw specifically impacts Firefox browsers due to how the browser interprets the end tag of SCRIPT elements in conjunction with the improperly encoded data, creating an exploitable condition for XSS attacks. The vulnerability operates at the application layer and requires no special privileges to exploit, making it particularly dangerous in web applications that rely on this library for JSON processing.
The operational impact of this vulnerability extends beyond simple data corruption or display issues, as it enables attackers to execute arbitrary JavaScript code within the context of a victim's browser session. This capability allows for session hijacking, data theft, redirection to malicious sites, and other malicious activities that compromise user security and application integrity. The vulnerability is particularly concerning in web applications that process user input through the python-cjson library, as it provides a direct pathway for attackers to bypass client-side security measures and inject malicious payloads that can persist across user sessions. The ease of exploitation makes this vulnerability attractive to threat actors seeking to compromise web applications without requiring advanced technical skills or privileged access.
Mitigation strategies for CVE-2009-4924 should prioritize immediate library updates to versions that properly handle forward slash characters in JSON encoding operations, as this represents the most effective solution to address the root cause. Organizations should implement comprehensive input validation and sanitization measures to prevent malicious data from entering the encoding pipeline, while also considering the adoption of more robust JSON libraries that have been thoroughly tested for security vulnerabilities. Network-based protections such as web application firewalls can provide additional layers of defense by monitoring for suspicious patterns in JSON data that may indicate exploitation attempts. The vulnerability aligns with CWE-79, which describes cross-site scripting flaws, and represents a specific implementation weakness that can be addressed through proper code review and security testing practices. Organizations should also consider implementing content security policies to limit the execution of unauthorized scripts and reduce the potential impact of successful exploitation attempts.