Vulnerability · Published Aug 5, 2026 · Assigned by TuranSec
CVE-2026-71263FreeModbus LINUXTCP Port Off-by-One Global Buffer Overflow in xMBPortTCPPool()
Critical 9.1
In plain English
A critical-severity out-of-bounds write in FreeModbus from cwalter-at. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities).
Severity (CVSS 3.1)9.1Critical
Exploit odds (30 days)0.5%top 56.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
The LINUXTCP port of FreeModbus contains an off-by-one bounds check in xMBPortTCPPool (demo/LINUXTCP/port/porttcp.c). The check uses a strict greater-than comparison instead of greater-than-or-equal against the 263-byte MB_TCP_BUF_SIZE limit.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| cwalter-at | FreeModbus | 0 – through * |
Weakness: CWE-787 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
References
- https://github.com/cwalter-at/freemodbus third-party-advisory
- https://github.com/cwalter-at/freemodbus/blob/master/demo/LINUXTCP/port/porttcp.c third-party-advisory