CVE-2023-51767 identifies a vulnerability in OpenSSH versions through 10.0 related to susceptibility to row hammer attacks on DRAM memory. Row hammer is a hardware-based fault injection technique where repeatedly accessing (hammering) certain rows of DRAM can induce bit flips in adjacent memory rows. In this case, the vulnerability concerns the integer value of the 'authenticated' variable in the mm_answer_authpassword function, which is used to determine if a user has successfully authenticated. Because this integer does not have protections against single-bit flips, an attacker who can induce a bit flip via row hammer could potentially alter the authentication state, effectively bypassing authentication checks. This attack requires a threat model where the attacker and victim are co-located on the same physical machine, and the attacker already has user-level privileges, which limits the attack surface. The supplier has disputed the applicability of this vulnerability, arguing that defending against hardware architectural weaknesses is outside the scope of the application. No CVSS score has been assigned, and no patches or known exploits are currently available. This vulnerability exemplifies a hardware-software interaction risk, where software security assumptions are undermined by physical memory fault injection techniques. It is particularly relevant in environments such as cloud or virtualized infrastructures where multiple tenants share hardware resources. The lack of mitigation at the application level means that defenses must focus on hardware protections, system configuration, and limiting attacker co-location opportunities.

For European organizations, the impact of CVE-2023-51767 depends heavily on their deployment environments. Organizations using OpenSSH in multi-tenant or virtualized settings, such as cloud service providers, hosting providers, or enterprises employing containerized or virtualized infrastructure, could be at risk if an attacker gains user-level access on the same physical host. Successful exploitation could allow attackers to bypass SSH authentication, leading to unauthorized access to critical systems, data breaches, and lateral movement within networks. This could compromise confidentiality and integrity of sensitive information and disrupt availability if attackers escalate privileges or deploy further attacks. However, the requirement for physical co-location and user privileges significantly limits the scope and ease of exploitation. Organizations relying on dedicated hardware or isolated environments face lower risk. The dispute by the supplier and absence of known exploits suggest the threat is currently theoretical but warrants attention in high-security environments. European sectors with high-value targets such as finance, government, and critical infrastructure using OpenSSH extensively should consider this vulnerability in their risk assessments.

Mitigation of CVE-2023-51767 requires a multi-layered approach beyond generic advice. First, organizations should minimize attacker co-location risk by avoiding multi-tenant deployments where untrusted users share physical hardware, or by employing strong tenant isolation techniques such as hardware-enforced virtualization extensions and memory protection technologies (e.g., Intel SGX, AMD SEV). Second, enable and enforce hardware-level protections against row hammer attacks, such as using ECC (Error-Correcting Code) memory, deploying memory modules with row hammer mitigation features, or applying firmware updates that address row hammer vulnerabilities. Third, monitor and restrict user privileges rigorously to prevent attackers from gaining any user-level access on critical hosts. Fourth, consider deploying runtime integrity checks or hardened OpenSSH builds that could detect or mitigate abnormal authentication state changes, although no official patches exist yet. Finally, maintain up-to-date system firmware and hardware drivers, and follow vendor advisories for any emerging mitigations. Regular security audits and penetration testing focused on co-location and side-channel attack vectors can also help identify exposure.