CVE-2026-77120: OS Command Injection Privilege Escalation

CVE-2026-77120 Overview

CVE-2026-77120 is an OS command injection vulnerability [CWE-78] affecting a Schneider Electric product with an SSH-accessible operating system console. The flaw allows an authenticated user to inject shell metacharacters into console input that is passed to the underlying operating system without proper neutralization. Successful exploitation results in privilege escalation to root and unauthorized execution of administrative functions on the affected device.

Critical Impact
An authenticated local attacker with SSH access can escape the restricted console and execute arbitrary commands as root, gaining full administrative control of the affected device.

Affected Products

Schneider Electric product referenced in security notice SEVD-2026-251-02
Devices with the operating system console reachable over SSH
Specific product versions listed in the vendor advisory

Discovery Timeline

2026-09-09 - CVE CVE-2026-77120 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-77120

Vulnerability Analysis

The vulnerability arises in an operating system console exposed over SSH on the affected device. The console accepts user input intended for a restricted administrative interface and passes portions of that input to underlying OS command invocations without adequate sanitization or escaping.

Because the console executes with elevated privileges, injected commands run as root. An authenticated attacker can therefore break out of the intended command surface, execute arbitrary binaries, modify system files, and perform administrative actions the account was never authorized to invoke. The attack requires local (SSH) access and valid high-privileged credentials, but no user interaction beyond the attacker's own session.

Root Cause

The root cause is improper neutralization of special elements used in an OS command [CWE-78]. The console builds command strings using user-controlled input and hands them to a shell interpreter or equivalent execution path. Shell metacharacters such as ;, |, &&, backticks, and $(...) are not filtered or escaped, allowing attacker-supplied fragments to be interpreted as additional commands.

Attack Vector

An attacker with valid credentials authenticates to the device over SSH and reaches the operating system console. The attacker then supplies input containing shell metacharacters to a console command that internally invokes an OS-level utility. The injected payload executes in the context of the console process, which runs as root, yielding full administrative access.

No verified proof-of-concept code has been published. Refer to the Schneider Electric Security Notice SEVD-2026-251-02 for vendor-supplied technical details.

Detection Methods for CVE-2026-77120

Indicators of Compromise

Unexpected root-owned processes spawned as children of the SSH or console service.
Shell metacharacters (;, |, `, $() present in console command audit logs.
New or modified files in system directories following interactive SSH sessions by non-root accounts.
SSH sessions from high-privileged administrative accounts at unusual times or from unexpected sources.

Detection Strategies

Enable and forward SSH authentication and session logs from the device to a centralized log store for analysis.
Alert on command-line arguments containing shell control characters submitted through the administrative console.
Correlate SSH login events with subsequent creation of privileged processes not associated with normal administrative workflows.

Monitoring Recommendations

Monitor SSH access to affected devices and restrict source IP ranges to trusted management networks.
Track configuration changes and account modifications on the device against an approved change baseline.
Review authentication logs for repeated or off-hours logins by accounts with console privileges.

How to Mitigate CVE-2026-77120

Immediate Actions Required

Apply the vendor patch or firmware update referenced in SEVD-2026-251-02 as soon as it is validated for the environment.
Disable SSH access on affected devices where it is not operationally required.
Rotate credentials for all high-privileged accounts that could reach the operating system console.
Restrict management-plane connectivity to a dedicated administrative VLAN or jump host.

Patch Information

Schneider Electric has published remediation guidance in the Schneider Electric Security Notice SEVD-2026-251-02. Consult the notice for the exact fixed versions and product identifiers before deploying updates.

Workarounds

Disable the SSH service on the device until the patch can be applied.
Limit high-privileged account access to a small number of vetted administrators.
Place affected devices behind a firewall that blocks inbound SSH from untrusted networks.
Enforce network segmentation to isolate operational technology assets from general enterprise traffic.

bash

# Configuration example: restrict SSH to a management subnet
# (adapt to the affected device's supported ACL syntax)
access-list MGMT permit tcp 10.10.20.0/24 any eq 22
access-list MGMT deny   tcp any any eq 22