SIMATIC WinCC Unified EUVD-2026-35382

Exploitation requires local access (AV:L) to a Windows host running SIMATIC WinCC Unified PC Runtime V16 through V21 prior to Update 2 with the WinCC Certificate Manager component installed, but needs no authentication to the application (PR:N), no user interaction (UI:N), and no special attack prerequisites (AT:N) - meaning any user or process that can read the relevant filesystem location on the runtime host can extract the key material. Limiting factors are that the attacker must already have a foothold on the HMI/engineering workstation itself (network-only attackers cannot reach the vulnerable storage), and impact is scoped to confidentiality of certificate material rather than direct code execution or runtime takeover.

The CVSS 4.0 vector (AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/SC:H) yields 8.2 because while the attack vector is local and requires no privileges or interaction, the impact is high confidentiality loss with a scope change into subsequent systems - consistent with stolen PKI material being reusable elsewhere on the OT network. EPSS and KEV are not reported, and no public PoC was identified, so weaponized mass exploitation is unlikely; the realistic threat is a malicious insider, a contractor with workstation access, or commodity malware on an engineering workstation pivoting into the controls network. This should be treated as a meaningful OT priority despite no active-exploitation signals, because key material compromise is persistent (rotating certificates is operationally expensive) and the CVSS 'subsequent system' impact reflects genuine lateral-movement risk in ICS environments.

A contractor or attacker with interactive access to a WinCC Unified engineering workstation - obtained via phishing-delivered malware, stolen RDP credentials, or physical access during maintenance - locates the Certificate Manager's key storage on disk and copies the unprotected key material to portable media or an attacker-controlled share. The stolen keys are then reused to sign or authenticate as a trusted runtime component, enabling impersonation of legitimate HMI traffic or decryption of captured protocol exchanges on the plant network. No public PoC is required because the weakness is filesystem-level disclosure rather than a memory-corruption primitive.