Cisco Warns of regreSSHion RCE Impacting Multiple Products

Cisco has issued a security advisory regarding a critical remote code execution (RCE) vulnerability, dubbed “regreSSHion,” that affects multiple products.

The vulnerability tracked as CVE-2024-6387, was disclosed by the Qualys Threat Research Unit on July 1, 2024. It impacts the OpenSSH server (sshd) in glibc-based Linux systems and has the potential to allow unauthenticated attackers to gain root access to affected systems.

Vulnerability Details

The regreSSHion vulnerability is a regression of an older flaw (CVE-2006-5051) that was reintroduced in OpenSSH version 8.5p1, released in October 2020.

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The flaw involves a race condition in the sshd’s SIGALRM handler, which calls functions that are not async-signal-safe, such as syslog().

An attacker can exploit this by opening multiple connections and failing to authenticate within the LoginGraceTime period, triggering the vulnerable signal handler asynchronously.

Cisco has identified several products across various categories affected by this vulnerability.

The company is actively investigating its product line to determine the full scope of impacted devices. The following table lists the affected products and their respective Cisco Bug IDs:

Mitigation and Recommendations

Cisco recommends several steps to mitigate the risk of exploitation:

• Restrict SSH Access: Limit SSH access to trusted hosts only. This can be achieved by applying infrastructure access control lists (ACLs) to prevent unauthorized access to SSH services.
• Upgrade OpenSSH: Upgrade to the latest patched version of OpenSSH (9.8p1) as soon as it becomes available in the package repositories of Linux distributions.
• Adjust LoginGraceTime: Set the LoginGraceTime parameter to 0 in the sshd configuration file to prevent the race condition, although this may lead to denial-of-service if all connection slots become occupied[1][6][7].

The Cisco Product Security Incident Response Team (PSIRT) knows that a proof-of-concept exploit code is available for this vulnerability. However, the exploitation requires customization, and there have been no reports of malicious use.

Cisco continues to assess all products and services for impact and will update the advisory as new information becomes available.

The regreSSHion vulnerability poses a significant risk to a wide range of Cisco products.

Customers are urged to follow Cisco’s recommendations and apply the necessary patches and mitigations to protect their systems from potential exploitation.

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