Zyxel Network Attached Storage (NAS) devices have received a security update to patch a critical severity command injection vulnerability. Devices affected by this flaw include NAS326 models running firmware version V5.21(AAZF.13)C0 or prior, NAS540 models running firmware version V5.21(AATB.10)C0 or prior, and NAS542 models running firmware version V5.21(ABAG.10)C0 or prior. In their security advisory, Zyxel do not offer any mitigation advice or workarounds, instead advising users to install the new patches to fix this flaw. Users should therefor apply the relevant patches for their devices as soon as possible to manage this vulnerability, the links for which are available in the Zyxel security advisory.  

Tracked as CVE-2023-27992 this critical severity vulnerability has been assigned a CVSS base score of 9.8. Although not currently known to be exploited with no proof of concept (PoC) code available, the critical severity rating assigned to this flaw means users and administrators should apply the new patches as soon as possible. This command injection vulnerability can potentially be exploited by remote, unauthenticated attackers, who can create and send a HTTP request to the vulnerable device. This will then allow the attackers access to execute arbitrary operating system (OS) commands remotely.  

Just last month Zyxel had to address critical vulnerabilities in their firewall and VPN products, followed shortly by another flaw, CVE-2023-28771, which was actively exploited in Mirai-like botnet attacks. This critical severity flaw with a CVSS base score of 9.8 was added to CISA’s Known Exploited Vulnerabilities Catalog at the end of May, at the same time as CISA issued a security alert about this flaw. A remote, unauthenticated attacker could exploit this flaw similarly to the NAS device flaw and execute OS commands through sending a maliciously crafted IKEv2 packet to UDP port 500 on the vulnerable devices. This exploit has publicly known PoC code so other botnets and DDoS attacks can be expected to take place. Users should therefore update their Zyxel firewall and VPN devices to the latest firmware release versions as soon as possible to avoid these attacks.