CVE-2015-7392 in FreeSWITCH
Summary
by MITRE
Heap-based buffer overflow in the parse_string function in libs/esl/src/esl_json.c in FreeSWITCH before 1.4.23 and 1.6.x before 1.6.2 allows remote attackers to execute arbitrary code via a trailing \u in a json string to cJSON_Parse.
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Analysis
by VulDB Data Team • 06/20/2022
The vulnerability CVE-2015-7392 represents a critical heap-based buffer overflow in the FreeSWITCH telecommunications platform that affects versions prior to 1.4.23 and 1.6.x prior to 1.6.2. This flaw exists within the parse_string function located in the esl_json.c file within the libs/esl/src directory of the FreeSWITCH source code. The vulnerability specifically manifests when processing JSON strings containing a trailing backslash followed by a 'u' character sequence, which is commonly used to represent Unicode escape sequences in JSON formatting standards. The issue arises from insufficient input validation and boundary checking during the parsing of JSON data structures, creating a condition where maliciously crafted JSON payloads can overwrite adjacent memory locations on the heap.
The technical exploitation of this vulnerability occurs through the cJSON_Parse function which is responsible for parsing JSON strings into structured data objects. When a JSON string contains a trailing \u sequence that does not conform to proper Unicode escape sequence formatting, the parse_string function fails to properly validate the input boundaries. This allows attackers to manipulate the heap memory layout by writing beyond the allocated buffer boundaries, potentially overwriting critical data structures, function pointers, or return addresses. The vulnerability maps to CWE-121, heap-based buffer overflow, and aligns with ATT&CK technique T1059.007 for execution through command and script interpreters, as successful exploitation could lead to arbitrary code execution on the target system. The attack vector is remote, meaning an attacker can trigger the vulnerability through network-based JSON input without requiring local access to the system.
The operational impact of this vulnerability extends beyond simple code execution, as it can potentially allow attackers to gain full control over the FreeSWITCH server, which serves as a core component in many telecommunications infrastructure deployments. FreeSWITCH is commonly used in VoIP gateways, PBX systems, and communication platforms where it handles sensitive voice and data traffic. Successful exploitation could result in complete system compromise, data exfiltration, service disruption, or the ability to intercept and manipulate voice communications. The vulnerability affects organizations that rely on FreeSWITCH for their telephony infrastructure, particularly those with exposed JSON APIs or those processing external JSON data from web services, SIP endpoints, or other network sources. The risk is compounded by the fact that FreeSWITCH is widely deployed in enterprise environments where it may be directly exposed to untrusted network traffic, making it an attractive target for remote exploitation attempts.
Organizations should implement immediate mitigations including upgrading to FreeSWITCH versions 1.4.23 or 1.6.2 and later, which contain the necessary patches to address the buffer overflow condition. Network segmentation and access controls should be enforced to limit exposure of FreeSWITCH components to untrusted networks, while input validation should be strengthened at all JSON parsing interfaces. The implementation of security monitoring and intrusion detection systems can help identify potential exploitation attempts by monitoring for unusual JSON parsing patterns or memory access anomalies. Additionally, organizations should conduct thorough vulnerability assessments of their FreeSWITCH deployments and review all JSON input handling code to identify similar buffer overflow conditions that may exist in custom modules or extensions. Regular security updates and patch management processes should be established to ensure timely deployment of security fixes, as this vulnerability demonstrates the importance of maintaining current software versions in telecommunications infrastructure environments.