CVE-2026-27556: Local File Inclusion RCE Vulnerability

CVE-2026-27556 Overview

CVE-2026-27556 is a Local File Inclusion (LFI) vulnerability that allows arbitrary PHP code execution on affected devices. The flaw resides in the /index.php/ajax/save_iodd_parameters endpoint. A low-privileged remote attacker holding a valid operator cookie can exploit the endpoint to include and execute attacker-controlled PHP files. The weakness is classified as [CWE-98] (Improper Control of Filename for Include/Require Statement in PHP Program).

Critical Impact
An authenticated operator-level attacker can achieve remote code execution, gaining full compromise of the affected device with impact on confidentiality, integrity, and availability.

Affected Products

Products covered by CERT@VDE advisory VDE-2026-014
Products covered by CERT@VDE advisory VDE-2026-027
Products covered by CERT@VDE advisory VDE-2026-028

Discovery Timeline

2026-09-16 - CVE-2026-27556 published to the National Vulnerability Database (NVD)
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-27556

Vulnerability Analysis

The vulnerability exists in the save_iodd_parameters AJAX handler exposed at /index.php/ajax/save_iodd_parameters. The endpoint accepts parameters that are passed into a PHP include or require statement without adequate validation. An authenticated user with an operator cookie can supply a path referencing an attacker-controlled file already present on the device. Once included, the PHP interpreter executes the file contents, giving the attacker code execution within the web application context.

The attack is reachable over the network, requires low complexity, and requires only operator-level credentials. There is no user interaction requirement. Successful exploitation results in full compromise of confidentiality, integrity, and availability on the target device.

Root Cause

The root cause is improper control of a filename used in a PHP include statement, tracked under [CWE-98]. The save_iodd_parameters handler trusts a client-supplied parameter and uses it to construct a path passed to a dynamic file inclusion call. Missing allow-list validation and missing path canonicalization let an attacker traverse the filesystem or reference uploaded content as executable PHP.

Attack Vector

Exploitation requires an authenticated session with an operator cookie. The attacker sends a crafted HTTP request to /index.php/ajax/save_iodd_parameters containing a manipulated file path parameter. The server includes the referenced file and executes any PHP code it contains. Attackers typically combine LFI with a prior file upload, log poisoning, or session data injection to plant PHP payloads that the include statement then executes.

No public exploit code or proof-of-concept has been published for this issue at the time of writing. Refer to the CERT@VDE Advisory VDE-2026-014 for vendor-specific technical detail.

Detection Methods for CVE-2026-27556

Indicators of Compromise

HTTP POST or GET requests to /index.php/ajax/save_iodd_parameters containing path traversal sequences such as ../, absolute paths, or references to unusual .php files.
Unexpected PHP files appearing in web-writable directories or upload directories on the device.
Web server processes spawning shells, network connections to unfamiliar hosts, or executing binaries after requests to the vulnerable endpoint.
Operator account activity from unusual source IP addresses or at unusual times.

Detection Strategies

Inspect web server access logs for requests to save_iodd_parameters with suspicious parameter values, particularly those containing filesystem paths or traversal sequences.
Correlate authenticated operator sessions with subsequent process creation events on the underlying host to identify post-exploitation activity.
Deploy application-layer signatures that flag LFI patterns targeting PHP endpoints served by the affected devices.

Monitoring Recommendations

Forward web application, authentication, and host process logs to a central analytics platform for correlation and retention.
Alert on new or modified PHP files in web-accessible directories on affected devices.
Monitor outbound network traffic from device management interfaces for connections to unexpected destinations.

How to Mitigate CVE-2026-27556

Immediate Actions Required

Restrict network access to device management interfaces so only trusted management stations can reach the web application.
Rotate operator credentials and review operator account membership to remove unused or shared accounts.
Review web server and authentication logs for prior requests to /index.php/ajax/save_iodd_parameters that reference unexpected file paths.

Patch Information

Refer to the CERT@VDE advisories for the affected vendor's fixed versions and update instructions: CERT@VDE Advisory VDE-2026-014, CERT@VDE Advisory VDE-2026-027, and CERT@VDE Advisory VDE-2026-028. Apply the vendor-provided firmware update on all affected devices.

Workarounds

Place affected devices behind a network segmentation boundary or firewall that blocks untrusted access to the HTTP management interface.
Disable or restrict operator-level web access where feasible until firmware updates are applied.
Enforce strong, unique operator passwords and multi-factor authentication on any upstream access path to the management interface.

bash

# Configuration example: restrict management interface access at the network edge
# Replace <mgmt_station_cidr> and <device_ip> with values for your environment
iptables -A INPUT -p tcp --dport 80 -s <mgmt_station_cidr> -d <device_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s <mgmt_station_cidr> -d <device_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -d <device_ip> -j DROP
iptables -A INPUT -p tcp --dport 443 -d <device_ip> -j DROP