CVE-2023-20109

CVE-2023-20109 is an out-of-bounds write (CWE-787) in the Group Encrypted Transport VPN (GET VPN) feature of Cisco IOS and Cisco IOS XE, caused by insufficient validation of Group Domain of Interpretation (GDOI) and G-IKEv2 protocol attributes. An authenticated, remote attacker with administrative control of either a GET VPN group member or key server can trigger the flaw by compromising the installed key server or by modifying a group member's configuration to point at an attacker-controlled key server, then sending crafted GDOI/G-IKEv2 attributes. A successful exploit allows the attacker to execute arbitrary code and gain full control of the device, or to crash/reload it, causing a denial-of-service condition. Only organizations running Cisco IOS/IOS XE devices with the GET VPN feature configured (as group members or key servers) are affected; CVSS 3.1 rates it 6.6 (medium) because exploitation requires high privileges and high attack complexity. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2023-10-10, indicating confirmed in-the-wild exploitation, while EPSS estimates a 2.3% probability of exploitation in the next 30 days and no public PoC is known.

What to do: Upgrade affected devices to a fixed release identified in Cisco's security advisory, and inventory GET VPN deployments with 'show crypto gdoi' to identify group members and their key servers. Because exploitation requires a compromised or attacker-controlled key server, harden and restrict access to key servers, verify that group member configurations point only to legitimate key servers, and rotate GET VPN keys if compromise is suspected. Per the CISA KEV required action, apply vendor mitigations promptly or discontinue use where mitigations are unavailable.