Linear eMerge E3-Series Physical Access Controller Remote Code Execution Vulnerability Analysis and Mitigation Guide (CVE-2019-7256)
Executive & SecOps Summary
SECOPS ASSESSMENTLinear eMerge E3-Series physical access control devices (versions 1.00-06 and prior)
Unauthenticated remote attackers can execute arbitrary system commands with root privileges by sending specially crafted HTTP requests
Immediately isolate vulnerable devices from the public internet and restrict access using strict firewall rules or apply the latest firmware updates
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Contact the manufacturer (Nortek/Linear) to obtain and apply the latest secure firmware update that addresses this command injection vulnerability. Ensure all devices are upgraded via the official administration console.
2. Temporary Workaround & Hardening Configuration
Immediately remove the device from the public-facing internet. Implement strict Access Control Lists (ACLs) or firewall rules to restrict access to the web management interface (ports 80 and 443) only to trusted administrative IP addresses.
# Block public access to the eMerge controller and allow only trusted admin subnet (e.g., 10.10.10.0/24)
iptables -A INPUT -p tcp -s 10.10.10.0/24 --dport 80 -j ACCEPT
iptables -A INPUT -p tcp -s 10.10.10.0/24 --dport 443 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP3. Log Audit & IoC Verification Commands
Scan web server access logs for suspicious requests targeting the vulnerable PHP endpoints containing command execution patterns.
# Search web access logs for command injection attempts targeting card_scan endpoints
grep -Ei 'card_scan.*(php|decoder)' /var/log/httpd/access_log /var/log/nginx/access.log 2>/dev/null | grep -E '(%3B|%7C|%60|;|\||`|cat|wget|curl|sh)'Stop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2019-7256) is a critical OS Command Injection (CWE-78) vulnerability in the Linear eMerge E3-Series physical access control systems. The root cause lies in the web management interface's PHP scripts, such as card_scan.php and card_scan_decoder.php, which fail to properly sanitize or validate user-supplied input before passing it to system shell execution functions.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated attacker can exploit this vulnerability by sending HTTP GET or POST requests containing shell metacharacters (such as ;, |, or ` `) within parameters like macheaders or reader`. Because the application directly concatenates these parameters into system commands, the injected commands are executed on the underlying Linux operating system with administrative (root) privileges. Due to the availability of public exploits and active exploitation by botnets, this vulnerability is listed in the CISA KEV catalog.
3. Infrastructure & Business Impact
Compromising a physical access control system allows remote attackers to physically unlock or lock facility doors, completely bypassing physical security controls. Furthermore, attackers can exfiltrate sensitive credential databases, access logs, and leverage the compromised device as a pivot point to lateral move into internal OT/ICS or corporate IT networks.
Official Vendor Advisories & References
Linear eMerge E3-Series devices allow Command Injections.
Frequently Asked SecOps Questions (CVE-2019-7256)
FAQQ1. How critical is CVE-2019-7256 and is it actively exploited in the wild?
CVE-2019-7256 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 97.1%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2019-7256?
Primary impacted vendors include nortek, linear across emerge e3-series. Scope summary: All Linear eMerge E3-Series Access Controller devices running version 1.00-06 or earlier
Q3. What temporary mitigations or workarounds exist for CVE-2019-7256 before patching?
[Mitigation] Immediately isolate vulnerable devices from the public internet and restrict access using strict firewall rules or apply the latest firmware updates Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2019-7256
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