CVE-2026-71263
CRITICAL
9,1
Source: 309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c
Attack Vector: network
Attack Complexity: low
Privileges Required: none
User Interaction: none
Scope: unchanged
Confidentiality: none
Integrity: high
Availability: high
Description
AI Translation Available
The LINUXTCP port of FreeModbus contains an off-by-one bounds check in xMBPortTCPPool() (demo/LINUXTCP/port/porttcp.c). The check `if (usTCPFrameBytesLeft > MB_TCP_BUF_SIZE)` uses a strict greater-than comparison instead of greater-than-or-equal against the 263-byte MB_TCP_BUF_SIZE limit. An MBAP frame with a Length field of 264 makes usTCPFrameBytesLeft equal to 263, which passes the flawed check, and the subsequent recv() call writes up to 263 bytes starting at buffer offset 7 into the 263-byte static buffer aucTCPBuf, overflowing it by 7 bytes into the adjacent static variable usTCPBufPos. A single crafted, unauthenticated Modbus TCP packet triggers the overflow, since Modbus has no built-in authentication.
787
Out-of-bounds Write
DraftCommon Consequences
Security Scopes Affected:
Integrity
Availability
Other
Potential Impacts:
Modify Memory
Execute Unauthorized Code Or Commands
Dos: Crash, Exit, Or Restart
Unexpected State
Applicable Platforms
Languages:
Memory-Unsafe, C, C++, Assembly
Technologies:
ICS/OT
https://github.com/cwalter-at/freemodbus
https://github.com/cwalter-at/freemodbus/blob/master/demo/LINUXTCP/port/porttcp…