CVE-2021-3156

CVE-2021-3156 is an off-by-one error (CWE-193) in the Unix Sudo utility that causes a heap-based buffer overflow (CWE-122) in Sudo's handling of command-line arguments. It is triggered locally when an unprivileged user invokes Sudo with specially crafted arguments, requiring no special privileges or non-default configuration. A successful exploit allows the attacker to execute arbitrary code as root, achieving full local privilege escalation on the host. Any Linux, Unix, or other system running a vulnerable version of Sudo is affected, and because Sudo ships by default on virtually all such systems the potential footprint is enormous. The flaw is listed in CISA's Known Exploited Vulnerabilities catalog (added 2022-04-06) and carries a 100% EPSS probability of exploitation within 30 days, indicating active in-the-wild exploitation, though specific ransomware use is unknown.

What to do: Upgrade Sudo to a patched release (1.9.5p2 or later, or the vendor-supplied update for your distribution) per vendor instructions, as required by the CISA KEV listing. Audit all Unix-like hosts by checking the installed Sudo version through your package manager and prioritize patching multi-user and internet-facing servers. Restricting local shell access and monitoring for anomalous Sudo invocations can reduce risk while patching completes.