CVE-2026-71254 nanoMODBUS Server-Side Out-of-Bounds Write in handle_read_file_record()
An out-of-bounds write in nanoMODBUS allows attackers to execute arbitrary code or cause denial of service via crafted Modbus requests.
- 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-2026-71254?
CVE-2026-71254 is a critical memory corruption vulnerability in debevv nanoMODBUS, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
nanoMODBUS through v1.23.0 contains an out-of-bounds write in the Modbus server-side handle_read_file_record function (FC 0x14, Read File Record) in nanomodbus.c. The function validates that the total request size does not exceed 245 bytes and that each sub-request's record_length is at most 124, but it never validates the CUMULATIVE response size across all sub-requests before processing them.
Weakness: CWE-787
Which versions are affected by CVE-2026-71254?
How do I fix CVE-2026-71254?
No fix has been published for CVE-2026-71254 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-2026-71254 being exploited?
There is no known exploitation of CVE-2026-71254 in the wild and no public exploit code.
Sources
Also known as GHSA-29rm-wvww-5gjv.