CVE-2026-115723 in Snap7
Summary
by MITRE • 10/23/2026
Snap7 through 1.4.3 contains an out-of-bounds write vulnerability in the passive partner that allows a malicious active partner to overflow application buffers by declaring an unvalidated BSend total length. Attackers connecting from the configured peer address can declare up to 65535 bytes and send a short fragment, causing BRecv to memcpy past the buffer and crash or corrupt SCADA, HMI or gateway processes.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/23/2026
The vulnerability identified in Snap7 versions through 1.4.3 represents a critical out-of-bounds write flaw within the passive partner implementation of the S7 communication protocol stack. This security defect arises from insufficient validation of input parameters during the handling of BSend requests, which are fundamental to data exchange between PLCs and client applications. In this architecture, an active partner initiates communication by declaring a total length for the data payload it intends to send. The flaw lies in the fact that Snap7 accepts these declared lengths without rigorous verification against actual buffer capacities or protocol constraints before proceeding with memory operations. This lack of validation creates a direct path for exploitation where an attacker can manipulate the size field to exceed safe boundaries, leading to severe memory corruption issues within the application process handling the connection.
From a technical perspective, the exploit mechanism involves sending a BSend request that specifies a total length significantly larger than the allocated buffer space, potentially up to 65535 bytes as permitted by the protocol's two-byte size field structure. However, instead of transmitting data matching this declared size, the attacker sends only a short fragment or malformed payload. When the passive partner processes this request, it attempts to execute a memcpy operation based on the unvalidated total length rather than the actual received data size. This discrepancy causes the memory copy function to write beyond the allocated buffer boundaries into adjacent memory regions. Such out-of-bounds writes can overwrite critical application state variables, return addresses, or other sensitive data structures stored in contiguous memory locations, fundamentally compromising the integrity of the running process.
The operational impact of this vulnerability is particularly severe given Snap7's widespread use in industrial control systems (ICS), Supervisory Control and Data Acquisition (SCADA) networks, Human-Machine Interface (HMI) applications, and various gateway devices. Because these environments often rely on continuous, real-time data processing with limited security isolation, a successful exploitation can lead to the immediate crash of critical processes or silent memory corruption that may cause erratic behavior later in operation. An attacker positioned as an active partner connecting from a configured peer address can trigger this condition remotely if network access controls are not strictly enforced. The resulting denial of service through process crashes disrupts industrial operations, while potential code execution via heap overflow techniques could allow full compromise of the underlying system, enabling further lateral movement within the OT network or manipulation of physical processes controlled by the PLC.
This vulnerability aligns with CWE-787: Out-of-bounds Write and CWE-20: Improper Input Validation, as it stems directly from failing to validate user-controlled input before using it in memory management operations. In terms of offensive security frameworks, this exploit scenario maps closely to MITRE ATT&CK technique T1496: Resource Hijacking or potentially T1530: Data from Cloud Storage if the corruption leads to data exfiltration via compromised state, though primarily it facilitates disruption consistent with Denial of Service tactics. The attack vector is classified as Network-based (T1078) requiring authentication only insofar as access to the configured peer address is granted, highlighting the importance of network segmentation and strict firewall rules for S7 ports which are often exposed beyond trusted zones due to legacy configurations or misconfigurations.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary defense is upgrading Snap7 to a version later than 1.4.3 where the developer has implemented proper bounds checking for BSend total lengths before initiating memory copy operations. Organizations should also enforce strict network segmentation using firewalls or industrial DMZs to restrict access to S7 ports exclusively from authorized active partners, thereby limiting the attack surface available to potential adversaries. Additionally, deploying intrusion detection systems capable of identifying anomalous protocol behavior, such as unusually large declared payload sizes followed by short actual transmissions, can provide early warning indicators for attempted exploitation. Regular security assessments and penetration testing focused on ICS protocols are essential to identify similar implementation flaws in other industrial software components that may share this pattern of inadequate input validation.