CVE-2026-66349 in libiec61850
Summary
by MITRE • 07/31/2026
The MMS server connection handler contains a flaw in its processing of BER-encoded request data. When an MMS confirmed request PDU containing an extended BER tag is received over an established session, the decoder may advance its internal buffer incorrectly due to a missing bounds check. This results in a one byte heap out-of-bounds read and causes the MMS service process to terminate, leading to a denial-of-service condition.
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Analysis
by VulDB Data Team • 07/31/2026
This vulnerability exists within the MMS server connection handler's processing of BER-encoded request data, representing a critical security flaw that can lead to service disruption. The issue manifests when the system receives an MMS confirmed request PDU containing an extended BER tag over an established session, creating a scenario where the decoder's internal buffer management fails to properly validate boundaries. The absence of proper bounds checking in the decoding process causes the buffer pointer to advance incorrectly, resulting in memory access violations that fundamentally compromise the service's stability.
The technical implementation flaw stems from improper buffer management during BER (Basic Encoding Rules) decoding operations, specifically when handling extended tag formats that require additional processing steps. This type of vulnerability aligns with CWE-129, which addresses insufficient bounds checking, and more specifically maps to CWE-787, concerning out-of-bounds write operations that can be extended to read scenarios. The heap-based out-of-bounds read occurs because the decoder does not properly validate the length of the extended tag data against available buffer space, allowing the parsing logic to access memory locations beyond the intended boundaries.
The operational impact of this vulnerability extends beyond simple service interruption, as it creates a reliable denial-of-service condition that can be exploited by remote attackers. The MMS service process termination represents a complete system failure scenario where legitimate users cannot establish or maintain connections to the messaging server, effectively blocking all communication through the affected service. This type of attack vector is particularly concerning in enterprise environments where MMS services may be integral to business operations and customer communications.
The vulnerability's exploitation potential aligns with ATT&CK technique T1499.004, which covers network denial-of-service attacks, and demonstrates how improper input validation can create system instability through memory corruption issues. Organizations should implement immediate mitigations including input validation controls that enforce strict bounds checking on all BER-encoded data, deployment of intrusion detection systems to monitor for malformed MMS requests, and application-level rate limiting to prevent exploitation through automated attack vectors. Additionally, the vulnerability highlights the importance of comprehensive buffer overflow protection mechanisms and proper memory management practices in network service applications.