On July 1st, 2024, the cybersecurity world was alerted to a significant vulnerability in the OpenSSH software known as RegreSSHion. Discovered by the Qualys Threat Research Unit, this family of security bugs allows an attacker to remotely execute code and potentially gain root access on machines running the OpenSSH server. Although not easily exploitable, the disclosure of RegreSSHion underscores the critical need for regular system updates and maintenance to prevent vulnerabilities from forming an exploit chain.
RegreSSHion affects OpenSSH versions from 8.5p1 (released March 3rd, 2021) to 9.7p1 (released March 11th, 2024), impacting over 14 million public-facing instances, predominantly on glibc-based Linux systems. Notably, systems running Windows and OpenBSD are not vulnerable to this attack. The vulnerability was patched in the 9.8/9.8p1 release on the same day it was disclosed, July 1st, 2024.
The root of the RegreSSHion vulnerability lies in a signal handler race condition within the server component of OpenSSH, known as sshd. This issue is triggered when a client fails to authenticate within the LoginGraceTime period (by default, 120 seconds). The sshd’s SIGALRM handler is then called asynchronously, invoking functions that are not safe for signal handlers, such as syslog(). In the affected versions, both the free() and malloc() functions are targeted within this signal handler, which can be exploited by an attacker.
Interestingly, RegreSSHion represents a regression of an older vulnerability, CVE-2006-5051, which had been mitigated in earlier versions of OpenSSH. The regression occurred when a crucial directive was accidentally removed in OpenSSH 8.5p1, reintroducing the vulnerability. This directive had previously transformed unsafe function calls into a safe _exit(1) call, effectively neutralizing the threat.
Qualys disclosed the vulnerability to OpenSSH developers on May 19th, 2024, and notified OpenWall on June 20th, 2024, before publicly announcing it on July 1st. The swift patching of the vulnerability highlights the responsiveness of the OpenSSH development team and the importance of timely disclosures in maintaining cybersecurity.
Despite the potential severity of RegreSSHion, it is not considered easily exploitable. However, this incident serves as a critical reminder of the importance of keeping systems updated. Regular updates ensure that known vulnerabilities are patched, reducing the risk of an attacker exploiting a combination of unpatched vulnerabilities to form a valid exploit chain.
Business owners and IT professionals should take this opportunity to reinforce their commitment to regular software updates and maintenance. While individual vulnerabilities might not pose an immediate threat, their presence in outdated systems can provide an entry point for more sophisticated attacks. Ensuring that all systems are up to date is a fundamental aspect of maintaining robust cybersecurity defenses.
The RegreSSHion vulnerability also illustrates the complex nature of software development and the potential for old vulnerabilities to resurface. This underscores the necessity for continuous vigilance and thorough testing in software updates. For businesses, it is a reminder of the importance of investing in reliable IT support and infrastructure capable of swiftly addressing and mitigating such issues.
In conclusion, while the RegreSSHion vulnerability may not be cause for immediate alarm due to its difficulty in exploitation, it highlights the broader imperative of maintaining updated and secure systems. Business owners should ensure their IT teams are proactive in applying updates and patches to prevent any potential vulnerabilities from being exploited. By doing so, they can protect their operations from disruption and safeguard their data and systems against emerging cyber threats.