CVE-2026-71263 FreeModbus LINUXTCP Port Off-by-One Global Buffer Overflow in xMBPortTCPPool()
An off-by-one error in FreeModbus's LINUXTCP port allows attackers to trigger a global buffer overflow, potentially leading to code execution or crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-71263?
CVE-2026-71263 is a critical memory corruption vulnerability in cwalter-at FreeModbus, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-787
Which versions are affected by CVE-2026-71263?
How do I fix CVE-2026-71263?
No fix has been published for CVE-2026-71263 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-71263 being exploited?
There is no known exploitation of CVE-2026-71263 in the wild and no public exploit code.
Sources
Also known as GHSA-cjvm-2pqq-6v6h.