CVE-2026-111280 in snap7
Summary
by MITRE • 10/16/2026
snap7 through 1.4.3 contains an out-of-bounds write vulnerability in TSnap7MicroClient::opReadArea() that allows malicious S7 peers to overflow client buffers via an unchecked DataLength field. Rogue or impersonated PLCs can return crafted ReadVar responses causing memcpy of up to 65535 bytes into caller buffers, crashing SCADA, HMI, or gateway processes and corrupting memory.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified in Snap7 versions through 1.4.3 represents a critical out-of-bounds write flaw located within the TSnap7MicroClient::opReadArea() function. This specific component is responsible for handling communication with Siemens S7 programmable logic controllers, which are ubiquitous in industrial control systems and SCADA environments. The root cause of this vulnerability lies in the improper validation of network input data, specifically regarding the DataLength field contained within responses from remote PLCs. In a secure implementation, any length parameter received from an external source must be rigorously validated against the size of the destination buffer before being used to determine how much data should be copied. However, Snap7 fails to perform this essential boundary check, allowing a malicious actor to exploit this oversight by manipulating network packets sent by compromised or rogue devices on the industrial network segment.
From an operational perspective, this flaw enables remote code execution scenarios that manifest as denial of service through buffer overflow and potential memory corruption. When a client initiates a read operation via opReadArea(), it allocates a fixed-size buffer to store the incoming data from the PLC. If a rogue or impersonated PLC returns a crafted ReadVar response with an artificially inflated DataLength field, the underlying memcpy function will proceed to copy up to 65535 bytes into this undersized caller buffer. This action results in writing data beyond the allocated memory boundaries, leading to immediate stack corruption and process crashes. In critical infrastructure environments where Snap7 is deployed as a gateway or communication bridge between SCADA systems and field devices, such crashes can cause significant downtime, disrupting monitoring and control capabilities essential for industrial operations.
The security implications of this vulnerability are severe due to the trust relationships inherent in Modbus TCP and S7 protocols commonly used in OT networks. Attackers who have gained access to the local network segment can impersonate legitimate PLCs or intercept traffic from compromised devices to inject these malformed responses. This aligns with MITRE ATT&CK techniques related to protocol manipulation and resource exhaustion, specifically leveraging weaknesses in input validation within industrial communication stacks. The ability to crash SCADA servers, HMI interfaces, or gateway processes effectively blinds the operational team to real-time plant conditions, creating a window for further exploitation or physical sabotage if redundant safety systems are not adequately isolated from the compromised network segment.
To mitigate this risk, organizations utilizing Snap7 must immediately upgrade to version 1.4.3 or later where the out-of-bounds write has been addressed through proper input validation and buffer size checks. Until an update can be applied in production environments, defensive measures should include strict network segmentation using industrial firewalls to restrict PLC-to-client communication only to authorized IP addresses. Additionally, implementing deep packet inspection on OT networks can help identify anomalous S7 protocol traffic with suspiciously large data length fields before they reach vulnerable clients. Monitoring for process crashes or unexpected restarts in SCADA and gateway services serves as a vital detection mechanism for ongoing exploitation attempts of this vulnerability.