BusyBox TLS ClientHello Buffer Overflow Vulnerability

Executive Summary

CVE-2026-88840 is a vulnerability in BusyBox's TLS implementation where the get_client_hello() function reads past the end of the input buffer when processing a truncated ClientHello message. This causes an out-of-bounds read that could expose sensitive data like cryptographic keys or memory addresses, or lead to crashes.

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Detection Guidance

Detecting this vulnerability requires checking if BusyBox's ssl_server applet is present and running on your system. Inspect running processes for ssl_server with commands like ps aux | grep ssl_server. Review BusyBox builds for the vulnerable networking/tls.c file. Monitor network traffic for truncated ClientHello messages, though this requires deep packet inspection.

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Impact Analysis

The vulnerability could allow an attacker to read sensitive memory contents, such as cryptographic keys or memory addresses, or cause the application to crash. It requires network access but no authentication or user interaction to exploit.

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Mitigation Strategies

Immediately stop using BusyBox's ssl_server in production environments. If ssl_server is in use, disable it and switch to a different TLS implementation. Apply patches if available from your vendor. Monitor systems for crashes or memory leaks that may indicate exploitation attempts.

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