Cisco IOS and IOS XE Software GET VPN Remote Code Execution and DoS Vulnerability (CVE-2023-20109)

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2023-20109) is an out-of-bounds write vulnerability (CWE-787) in the Group Encrypted Transport VPN (GET VPN) feature of Cisco IOS and Cisco IOS XE Software. The root cause lies in the insufficient validation of attributes within the Group Domain of Interpretation (GDOI) and G-IKEv2 protocols used for key management and policy distribution. An attacker can exploit this by sending crafted protocol packets that bypass boundary checks, leading to memory corruption.

2. Exploitation Mechanics & Attack Scenario

To exploit this vulnerability, an attacker must either compromise an existing key server or modify a group member's configuration to point to a rogue key server under the attacker's control. Once established, the attacker transmits malicious GDOI/G-IKEv2 key exchange payloads containing malformed attributes. When the target device processes these attributes, it triggers an out-of-bounds write, allowing the attacker to hijack the execution flow to run arbitrary code or crash the system, resulting in a Denial of Service (DoS).

3. Infrastructure & Business Impact

This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. A successful exploit grants the attacker full administrative control over critical routing and VPN gateway infrastructure. This can lead to complete network compromise, unauthorized decryption of VPN traffic, data exfiltration, and severe operational downtime.