CVE-2026-41020 in easyE4
Summary
by MITRE • 10/27/2026
Eaton easyE4 uses a static nonce during authentication, which could allow an unauthenticated attacker with access to captured authentication traffic to replay a valid authentication exchange and gain unauthorized access to the device.
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Analysis
by VulDB Data Team • 10/27/2026
The vulnerability identified in Eaton's easyE4 programmable logic controller involves a critical flaw in its authentication mechanism, specifically regarding the handling of nonces during the secure communication handshake. In modern cryptographic protocols, such as those based on Challenge-Response Authentication or mutual TLS variants used in industrial control systems, a nonce is intended to be a unique, random number generated for each session to ensure freshness and prevent replay attacks. However, analysis reveals that the easyE4 device utilizes a static, hardcoded, or predictable nonce value across all authentication exchanges rather than generating a fresh cryptographic challenge for every connection attempt. This fundamental deviation from secure design principles effectively neutralizes one of the primary defenses against traffic interception and reuse, leaving the integrity of the authentication process severely compromised.
From an operational perspective, this flaw allows any attacker who has network access to the industrial segment where the easyE4 resides to perform a replay attack. By capturing a valid authentication exchange between a legitimate client or management station and the controller, an adversary can record the encrypted credentials and associated metadata. Because the nonce does not change, the captured session data remains valid for subsequent use. The attacker can then inject this recorded traffic back into the network stream at any time, tricking the device into accepting it as a fresh, legitimate login attempt. This bypasses the need to crack passwords or exploit other software bugs, providing direct unauthorized access with minimal technical effort once initial packet capture capability is established within the local area network.
The impact of this vulnerability extends beyond simple unauthorized access; it threatens the availability and integrity of critical industrial processes. An attacker gaining control via replayed credentials can potentially reprogram logic routines, alter setpoints for sensors and actuators, or halt production lines entirely. In environments where safety is paramount, such as manufacturing plants or utility infrastructure, malicious manipulation of controller outputs could lead to physical damage, environmental hazards, or threats to human life. Furthermore, the persistence of this access allows for long-term stealthy monitoring and preparation for more sophisticated attacks, including those targeting interconnected systems in a broader industrial network topology.
This vulnerability aligns with CWE-328, which describes the use of static values where dynamic values are expected, specifically within cryptographic contexts to prevent replay attacks. It also maps directly to MITRE ATT&CK technique T1557, Adversary-in-the-Middle, as it facilitates man-in-the-middle scenarios by allowing an attacker to impersonate a legitimate user through traffic reuse rather than active decryption or modification of the payload itself. The lack of session uniqueness is a classic implementation error that undermines the confidentiality and authenticity guarantees provided by underlying encryption protocols.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. Eaton should release a firmware update that enforces the generation of cryptographically secure, random nonces for every authentication transaction, ensuring that each session is unique and time-bound. Until such patches are applied, network segmentation becomes critical; administrators should isolate easyE4 devices from untrusted networks using strict firewall rules or VLANs to limit exposure to potential attackers with packet capture capabilities. Additionally, implementing mutual authentication where both the client and server verify identities can reduce reliance on single-point credential validation. Regular monitoring of network traffic for anomalous patterns, such as repeated identical handshake sequences, may also help in detecting active exploitation attempts before significant damage occurs.