SonicWall Gen6 SSL-VPN incomplete-patching (CVE-2024-12802) — Akira-linked actors brute-force MFA via UPN/SAM account-name split, February–March 2026 intrusions

Threat actors whose TTPs are consistent with Akira ransomware activity successfully bypassed MFA on SonicWall Gen6 SSL-VPN appliances running officially-patched firmware between February and March 2026; SonicWall and incident-response vendors confirm the root cause is that the firmware update for CVE-2024-12802 (CVSS 9.1, AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N) does not by itself enforce MFA on both User Principal Name (user@domain) and SAM-account-name (DOMAIN\user) login formats — six additional manual LDAP-reconfiguration steps from SonicWall KB kA1VN0000000RBd0AM are required (Cybersecurity Dive, 2026-05-20; BleepingComputer, 2026-05-20). Attackers brute-forced credentials against the UPN login path — which accepts authentication without triggering MFA challenges when the LDAP reconfiguration is incomplete — at speed and without producing the standard authentication alerts; per BleepingComputer's reporting, intrusion responders observed sessions of 30 to 60 minutes during which attackers logged in, performed network reconnaissance, tested credential reuse on internal systems and logged out. Gen6 SSL-VPN reached end-of-life on 2026-04-16 and receives no further security updates; Gen7 and Gen8 are remediated by firmware update alone. Why it matters to us: the technique is a textbook example of why CVSS / vendor-advised patch status is insufficient operational signal — the appliance shows patched-firmware version, MFA appears enabled in the admin UI, and authentications succeed against an alternative account-name format that bypasses the policy enforcement entirely. Detection concept — SonicWall Gen6 SSL-VPN syslog filter for successful SSL-VPN authentications where the login field is UPN-format rather than SAM-format, especially from source IPs with high authentication-attempt volume; correlate with short-duration recon-and-credential-reuse sessions consistent with the 30-to-60-minute pattern BleepingComputer documents. Hardening — complete every step in SonicWall KB kA1VN0000000RBd0AM; given Gen6 EoL, migrate to Gen7/Gen8 on a defined cut-over timeline.