- The vulnerability is a regression of a previous issue (CVE-2006-5051) that was introduced in OpenSSH 8.5p1 in October 2020.
- The vulnerability allows for remote code execution as root on glibc-based Linux systems due to the SIGALRM handler calling non-async-signal-safe functions like syslog().
- Older vulnerable OpenSSH versions like 3.4p1 and 4.2p1 can be exploited by interrupting free() calls and leveraging heap corruption techniques like unlink() and House of Mind.
- Newer vulnerable versions like 9.2p1 can be exploited by interrupting malloc() calls and corrupting FILE structures to gain arbitrary code execution.
- Precise timing and network delay mitigation techniques are critical to winning the signal handler race condition.
- The exploit requires carefully crafting the heap layout and leveraging leftover data from previous allocations.
- OpenBSD is not vulnerable because it uses a safer syslog_r() function in its SIGALRM handler.
- The vulnerability is present in the default configuration of OpenSSH and affects the privileged sshd process.
- Significant effort and multiple iterations were required to develop reliable exploits for the different OpenSSH versions.
- The research demonstrates the continued need for vigilance in secure software development, as even a well-designed system like OpenSSH can have subtle regressions that introduce critical vulnerabilities.