CVE-2023-26067: Lexmark Cxtpc Firmware Input Validation

CVE-2023-26067 Overview

CVE-2023-26067 is a critical input validation vulnerability affecting a wide range of Lexmark printer devices with firmware dated through 2023-02-19. This vulnerability exists in the embedded web server of affected Lexmark printers and multifunction devices, where improper input validation allows remote attackers to potentially execute arbitrary code on vulnerable devices. The flaw represents the first of four related input validation issues identified in Lexmark device firmware.

Critical Impact

Remote attackers can exploit this input validation flaw to achieve code execution on vulnerable Lexmark printers, potentially compromising network security and enabling lateral movement within enterprise environments. The vulnerability is network-accessible without authentication requirements.

Affected Products

• Lexmark CX Series (CX930, CX931, CX942, CX943, CX944, CX730, CX735, CX820, CX825, CX827, CX920-CX924)
• Lexmark MX Series (MX432, MX931, MX331, MX431, MX321, MX421, MX521, MX522, MX622, MX721, MX722, MX725, MX822, MX826)
• Lexmark CS Series (CS943, CS331, CS431, CS439, CS421, CS521, CS720, CS725, CS727, CS728, CS820, CS827, CS921, CS923, CS927)
• Lexmark XC Series (XC9325, XC9335, XC9445, XC9455, XC9465, XC4342, XC4352, XC2326, XC2235, XC4240, XC6152, XC6153, XC8155, XC8160, XC8163, XC4140, XC4143, XC4150, XC4153, XC9225, XC9235, XC9245, XC9255, XC9265)
• Lexmark MS Series (MS331, MS431, MS439, MS321, MS421, MS521, MS621, MS622, MS725, MS821, MS822, MS823, MS825, MS826)
• Lexmark MB/MC Series (MB2236, MB3442, MB2338, MB2442, MB2546, MB2650, MB2770, MC3426, MC3224, MC3326, MC2535, MC2640, MC2325, MC2425)
• Multiple firmware variants including CXTPC, CSTPC, MXTCT, MXTPM, CXTMM, MSLSG, MXLSG, MSLBD, MXLBD, MSNGM, MXNGM, MXTGM, MSNGW, MSTGW, MXTGW, CSLBN, CSLBL, CXLBN, CXLBL, CSNZJ, CXTZJ, CXNZJ, CXTPP, CSTAT, CXTAT, CSTMH firmware

Discovery Timeline

• April 10, 2023 - CVE-2023-26067 published to NVD
• February 11, 2025 - Last updated in NVD database

Technical Details for CVE-2023-26067

Vulnerability Analysis

This vulnerability stems from improper input validation (CWE-20) in the embedded web server component of numerous Lexmark printer models. The vulnerability allows attackers to send specially crafted requests over the network that bypass input sanitization routines, potentially leading to remote code execution on the target device. The attack can be conducted remotely over the network without requiring user interaction, though successful exploitation requires high attack complexity, making it more challenging to reliably exploit.

The embedded web server, which provides administrative and management functionality for Lexmark devices, fails to properly validate certain input parameters. This architectural weakness in the input handling routines creates an attack surface that sophisticated attackers can leverage to inject and execute malicious code within the printer's operating environment.

Root Cause

The root cause of CVE-2023-26067 is improper input validation (CWE-20) in the firmware's embedded web server. The vulnerable code fails to adequately sanitize user-supplied input before processing, allowing attackers to inject malicious data that can alter program execution flow. This type of vulnerability typically occurs when input data is trusted without verification, passed directly to sensitive functions, or processed without boundary checking.

Attack Vector

The attack vector is network-based, targeting the embedded web server interface exposed by affected Lexmark printers. An attacker positioned on the same network (or with remote access to the printer's web interface) can craft malicious HTTP requests to exploit the input validation weakness.

The exploitation mechanism involves sending specially crafted data to the embedded web server that bypasses input validation checks. When processed by the vulnerable firmware component, this malformed input can lead to arbitrary code execution on the device. The Packet Storm security advisory provides technical details on the remote code execution exploitation chain targeting the embedded web server.

While the attack requires no authentication or user interaction, the high complexity rating indicates that reliable exploitation may require specific conditions or sophisticated techniques. Successful exploitation grants attackers full control over the printer device with potential to exfiltrate documents, intercept print jobs, or use the compromised device as a pivot point for further network attacks.

Detection Methods for CVE-2023-26067

Indicators of Compromise

• Unusual outbound network connections from printer devices to unexpected external IP addresses
• Anomalous HTTP request patterns targeting the embedded web server management interface
• Unexpected firmware modifications or configuration changes on Lexmark devices
• Suspicious print job activity or document exfiltration attempts originating from printer devices

Detection Strategies

• Implement network monitoring rules to detect malformed or suspicious HTTP requests targeting Lexmark printer web interfaces
• Deploy intrusion detection signatures that identify exploitation attempts matching known CVE-2023-26067 attack patterns
• Monitor printer device logs for authentication anomalies, unusual administrative actions, or error messages indicating input handling failures
• Conduct regular firmware version audits to identify unpatched Lexmark devices in the environment

Monitoring Recommendations

• Enable verbose logging on Lexmark device embedded web servers where supported
• Configure SIEM rules to alert on unusual network traffic patterns involving printer subnets
• Implement network segmentation to isolate printer devices and monitor inter-VLAN traffic for signs of lateral movement
• Schedule periodic vulnerability scans specifically targeting print infrastructure to track remediation progress

How to Mitigate CVE-2023-26067

Immediate Actions Required

• Apply the latest firmware updates from Lexmark that address CVE-2023-26067 to all affected devices immediately
• Restrict network access to printer embedded web servers using firewall rules and access control lists
• Disable unnecessary network services and remote management interfaces on affected Lexmark devices
• Implement network segmentation to isolate print infrastructure from critical network segments

Patch Information

Lexmark has released firmware updates to address this vulnerability. Organizations should consult the Lexmark Security Alert for CVE-2023-26067 for specific firmware versions and download links for affected models. Additionally, the Lexmark Security Alerts Support page provides ongoing updates and security advisories for all Lexmark products.

The firmware update process varies by model but typically involves downloading the appropriate firmware file from Lexmark's support portal, accessing the device's embedded web server administrative interface, and uploading the firmware update. Organizations with large printer fleets should leverage Lexmark's management tools for centralized firmware deployment.

Workarounds

• Disable the embedded web server on affected devices if remote management is not required
• Implement strict network ACLs to limit access to printer management interfaces to authorized administrative workstations only
• Deploy a web application firewall or reverse proxy in front of printer web interfaces to filter potentially malicious requests
• Consider air-gapping critical printers that handle sensitive documents until firmware updates can be applied

# Example network ACL configuration to restrict printer web access
# Restrict access to Lexmark embedded web server (port 80/443)
# Allow only from management VLAN (example: 10.0.100.0/24)
iptables -A INPUT -p tcp --dport 80 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP