Executive Summary

CVE-2025-51495 is an integer overflow vulnerability in the WebSocket component of the Mongoose library versions 7.5 through 7.17. It occurs in the function that handles incoming WebSocket frames (mg_ws_cb), where a specially crafted WebSocket request can cause the offset variable to underflow when calculating ofs-1, resulting in a very large value. This leads to out-of-bounds memory access during buffer manipulation, which can cause the application to crash or potentially lead to memory corruption or remote code execution if downstream vendors integrate the component improperly. The vulnerability was addressed by enhancing the validation logic for the offset parameter to prevent improper buffer deletion and mitigate risks such as buffer overflows and data corruption. [1, 2]

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Impact Analysis

This vulnerability can cause the affected application using the Mongoose WebSocket component to crash when processing specially crafted WebSocket requests. In some cases, if the component is integrated improperly by downstream vendors, it may lead to buffer overflows, memory corruption, and potentially remote code execution. This means an attacker could remotely exploit this flaw to disrupt service availability or execute arbitrary code on the affected system, posing significant security risks. [1, 2]

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Detection Guidance

This vulnerability can be detected by monitoring for crashes or abnormal behavior in applications using the Mongoose WebSocket component, especially when receiving WebSocket frames. A practical approach is to use the Mongoose 'websocket-server' example with AddressSanitizer (ASAN) enabled to reproduce the crash by sending specially crafted WebSocket packets. For detection on your system, you can use network traffic capture tools like Wireshark or tcpdump to identify suspicious WebSocket frames. Additionally, testing with a modified WebSocket client that sends crafted packets (similar to the proof of concept) can help detect the vulnerability. Specific commands include running the websocket-server example with ASAN enabled and using a custom websocket-client to send malicious frames to trigger the crash. [2]

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Mitigation Strategies

Immediate mitigation steps include updating the Mongoose library to a version that includes the patch improving offset validation in the WebSocket component (merged in pull request #3131). This patch enhances validation logic to prevent integer overflow and buffer overflows during fragmented WebSocket frame processing. If updating is not immediately possible, consider implementing input validation or filtering at the network perimeter to block suspicious WebSocket frames. Monitoring application logs for crashes related to WebSocket processing and applying vendor patches promptly are also recommended. [1]

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