CVE-2020-7566

Vulnerability

A CWE-334: Small Space of Random Values vulnerability exists in Schneider Electric Modicon M221 programmable logic controllers (all references, all versions). The random value space used in the encryption key generation between EcoStruxure Machine - Basic software and the controller is insufficiently large (too few possible values). This weakness reduces the cryptographic strength of the session, making brute‑force recovery of the key feasible [1].

Exploitation

An attacker must be on the same adjacent network as the controller and capture network traffic exchanged during the session initialization (a passive sniffing position). The attacker does not need authentication. User interaction is not required beyond normal operation. Once the encrypted traffic is captured, the attacker can brute‑force the limited‑size random value to recover the encryption key [1].

Impact

Successful exploitation allows the attacker to decrypt all subsequent communications between the programming software and the PLC. With the decrypted traffic, the attacker can obtain the password hash (related to CVE‑2020‑7567) and potentially gain unauthorized control over the PLC. This could lead to exposure of sensitive program data and configuration, and possible disruption or manipulation of the industrial process [1].

Mitigation

Schneider Electric has not released a firmware update to address this vulnerability as of the publication date. The vendor recommends users apply defense‑in‑depth measures, including network segmentation, use of VPNs for remote access, and restricting physical access to the control network. The product is not listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. Users should monitor Schneider Electric’s security advisories for future updates [1].