CVE-2023-20109 Overview
A vulnerability in the Cisco Group Encrypted Transport VPN (GET VPN) feature of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, remote attacker who has administrative control of either a group member or a key server to execute arbitrary code on an affected device or cause the device to crash. This vulnerability is due to insufficient validation of attributes in the Group Domain of Interpretation (GDOI) and G-IKEv2 protocols of the GET VPN feature.
An attacker could exploit this vulnerability by either compromising an installed key server or modifying the configuration of a group member to point to a key server that is controlled by the attacker. A successful exploit could allow the attacker to execute arbitrary code and gain full control of the affected system or cause the affected system to reload, resulting in a denial of service (DoS) condition.
Critical Impact
This vulnerability is actively exploited in the wild and has been added to the CISA Known Exploited Vulnerabilities (KEV) catalog. Attackers with administrative access to GET VPN infrastructure can achieve remote code execution or cause denial of service on affected Cisco network devices.
Affected Products
- Cisco IOS Software (versions 12.4 through 15.9)
- Cisco IOS XE Software (versions 3.3 through 17.11)
- Network devices configured with Group Encrypted Transport VPN (GET VPN) feature
Discovery Timeline
- September 27, 2023 - CVE CVE-2023-20109 published to NVD
- October 28, 2025 - Last updated in NVD database
Technical Details for CVE-2023-20109
Vulnerability Analysis
This out-of-bounds write vulnerability (CWE-787) affects the GET VPN feature implementation in Cisco IOS and IOS XE software. The vulnerability stems from improper validation of protocol attributes within two key encryption protocols: the Group Domain of Interpretation (GDOI) protocol and the G-IKEv2 protocol.
When processing GET VPN protocol messages, the affected software fails to properly validate input parameters, allowing maliciously crafted attribute values to trigger memory corruption. An attacker who has already gained administrative control over a key server or group member in the VPN infrastructure can leverage this position to send specially crafted protocol messages that write data beyond allocated memory boundaries.
The exploitation requires privileged access to GET VPN components, which limits the attack surface but also means that compromise of any administrative position in the VPN infrastructure can cascade to complete device takeover.
Root Cause
The root cause is insufficient validation of attributes in the GDOI and G-IKEv2 protocol implementations within the GET VPN feature. When processing security policy distribution or key exchange messages, the software does not adequately verify attribute lengths and values before writing data to memory buffers. This allows an attacker to craft protocol messages with malicious attribute values that cause out-of-bounds memory writes, leading to arbitrary code execution or device crashes.
Attack Vector
The attack requires an authenticated, remote attacker with one of the following positions:
Compromised Key Server: An attacker who has gained administrative control of a GET VPN key server can distribute malicious security policies containing crafted attributes to group members during normal protocol operations.
Reconfigured Group Member: An attacker who can modify the configuration of a group member can point it to an attacker-controlled key server, which then serves malicious protocol responses.
The attacker leverages the trust relationship between GET VPN components to deliver the exploit payload through legitimate protocol channels. Once the malicious attributes are processed, the out-of-bounds write can overwrite critical memory regions, enabling code execution with device-level privileges or triggering a device reload.
Detection Methods for CVE-2023-20109
Indicators of Compromise
- Unexpected device reloads or crashes on routers configured with GET VPN
- Anomalous GDOI or G-IKEv2 protocol traffic patterns between key servers and group members
- Unauthorized changes to GET VPN group member configurations, particularly key server addresses
- Evidence of compromised key server administrative credentials
- Unusual administrative access patterns to GET VPN infrastructure components
Detection Strategies
- Monitor syslog messages for unexpected device reloads correlating with GET VPN protocol activity
- Implement network traffic analysis to detect anomalous GDOI (UDP port 848) and G-IKEv2 traffic
- Audit GET VPN configurations for unauthorized key server address modifications
- Deploy intrusion detection signatures for malformed GET VPN protocol attributes
- Review authentication logs for suspicious administrative access to key servers and group members
Monitoring Recommendations
- Enable detailed logging for GET VPN protocol operations on all affected devices
- Configure SNMP traps for device reload events and correlate with VPN subsystem activity
- Implement configuration change monitoring to detect unauthorized modifications to GET VPN settings
- Establish baseline traffic patterns for GET VPN communications to identify deviations
How to Mitigate CVE-2023-20109
Immediate Actions Required
- Review the Cisco Security Advisory to determine if your software version is affected
- Prioritize patching given the active exploitation status and CISA KEV listing
- Audit administrative access controls for all GET VPN key servers and group members
- Verify the integrity of GET VPN configurations and key server address settings
- Implement network segmentation to limit exposure of GET VPN management interfaces
Patch Information
Cisco has released software updates that address this vulnerability. Organizations should upgrade to a fixed software release as documented in the Cisco Security Advisory. Due to the extensive version range affected (Cisco IOS 12.4 through 15.9 and IOS XE 3.3 through 17.11), administrators should carefully identify their current version and consult the advisory's fixed release information.
Given that this vulnerability is listed in the CISA Known Exploited Vulnerabilities Catalog, federal agencies and organizations following CISA guidance should prioritize remediation according to required timelines.
Workarounds
- Implement strict access controls limiting administrative access to key servers and group members
- Monitor and audit all GET VPN configuration changes through change management processes
- Consider network segmentation to isolate GET VPN infrastructure from potential attack vectors
- If GET VPN is not required, disable the feature on affected devices to eliminate the attack surface
# Verify GET VPN configuration status
show crypto gdoi
show crypto gkm
# Review key server configuration
show crypto gdoi ks members
show crypto gdoi ks policy
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
