CVE-2026-92853 in ThreadX
Summary
by MITRE • 10/20/2026
The TLS 1.3 Certificate-message parser in NetX Secure decrements the message length to skip a context byte without first establishing that the message has a byte to skip. A zero-length Certificate message therefore wraps the unsigned length to `0xFFFFFFFF`, which makes the bounds check that follows vacuous and sends the parser reading past the session packet buffer.
The trigger is a four-byte handshake header and requires no cryptographic validity. It is reachable pre-authentication.
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Analysis
by VulDB Data Team • 10/20/2026
The vulnerability identified in NetX Secure TLS 1.3 implementation represents a critical integer underflow condition within the Certificate-message parsing logic, specifically affecting the handling of context bytes during the handshake process. The core technical flaw stems from an improper validation sequence where the parser attempts to decrement the message length field by one byte to account for a context identifier before verifying that such a byte actually exists in the payload. This logical error means that if a client or server sends a Certificate message with a declared length of zero, the unsigned integer representing the remaining bytes wraps around from zero to four billion and twenty-three million five hundred eighty thousand seven hundred forty-seven (0xFFFFFFFF). Consequently, subsequent bounds checks that rely on this corrupted length value become effectively vacuous because they compare against an excessively large number rather than the actual buffer size. This allows the parser to proceed with reading data well beyond the allocated session packet buffer boundaries, leading to a heap-based or stack-based out-of-bounds read depending on the specific memory layout of the NetX Secure implementation.
From an operational perspective, this vulnerability is particularly severe due its reachability pre-authentication and lack of cryptographic requirements for exploitation. An attacker can trigger this condition by sending a malformed TLS handshake message consisting merely of a four-byte header indicating a Certificate message with zero length. Because no valid certificate chain or digital signature verification is required to reach the vulnerable code path, remote unauthenticated attackers can interact directly with the flaw during the initial connection establishment phase. The primary impact involves information disclosure through memory leakage, as the out-of-bounds read may expose sensitive data stored in adjacent memory regions such as private keys, session tokens, or other application-specific secrets. In more complex scenarios involving specific compiler optimizations and heap layouts, this could potentially lead to denial of service conditions if the invalid access triggers a segmentation fault or system crash within the network stack processing thread.
This vulnerability aligns with Common Weakness Enumeration (CWE) identifiers such as CWE-190 Integer Overflow or Wraparound and CWE-787 Out-of-bounds Read, reflecting both the arithmetic error in length handling and the resulting memory safety violation. In terms of attack vectors, it maps to MITRE ATT&CK techniques related to initial access via protocol vulnerabilities, specifically leveraging weaknesses in cryptographic implementations (T1592) or exploiting client-side processing flaws if this code is part of a server implementation that processes incoming handshakes. The lack of input validation prior to arithmetic operations highlights a fundamental gap in secure coding practices regarding boundary checks for variable-length fields in network protocols.
Mitigation strategies must focus on enforcing strict preconditions before performing any modifications to message length variables. Developers should implement explicit checks to ensure the message payload contains sufficient bytes to accommodate expected structural elements like context identifiers before attempting to decrement counters or adjust pointers. Additionally, incorporating fuzzing tests that specifically target edge cases in TLS handshake messages with zero-length payloads can help identify similar parsing flaws across different protocol states. For immediate remediation, applying vendor-provided patches is essential as they likely include the necessary validation logic to prevent integer wraparound and ensure bounds checks remain effective against malformed inputs.