CVE-2018-7791 Auth bypass in Modicon M221, all references, all versions prior to firmware V1.6.2.0

Critical 9.8 Published 29 Aug 2018 Updated 29 May 2026

Attackers can bypass authentication to overwrite passwords and upload original programs from the PLC.

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-2018-7791?

CVE-2018-7791 is a critical authentication bypass vulnerability in Schneider Electric SE Modicon M221, all references, all versions prior to firmware V1.6.2.0, published on 29 Aug 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

A Permissions, Privileges, and Access Control vulnerability exists in Schneider Electric's Modicon M221 product (all references, all versions prior to firmware V1.6.2.0). The vulnerability allows unauthorized users to overwrite the original password with their password. If an attacker exploits this vulnerability and overwrite the password, the attacker can upload the original program from the PLC.

Weakness: CWE-287, CWE-284

Which versions are affected by CVE-2018-7791?

It affects 1 product.

Products include Schneider-Electric Modicon M221 Firmware.

How do I fix CVE-2018-7791?

No fix has been published for CVE-2018-7791 yet. Limit exposure of the affected software until one is available.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

Is CVE-2018-7791 being exploited?

There is no known exploitation of CVE-2018-7791 in the wild and no public exploit code.

Sources

Also known as GHSA-ppc6-q8hw-556j.