Is CVE-2023-20109 (Cisco IOS and IOS XE Group Encrypted Transport VPN Out-of-Bounds Write) being exploited in the wild?

By NHI Mgmt Group Editorial Team Updated October 18, 2026 Domain: Threats, Abuse & Incident Response

Yes. CISA added CVE-2023-20109 to its Known Exploited Vulnerabilities catalogue on 10 October 2023, which it does only when there is reliable evidence of active exploitation. CISA has not linked it to known ransomware campaigns. Any organisation running the affected product should treat remediation as urgent. Check exposure first, then patch or mitigate, then review logs for signs of earlier compromise.

What “exploited in the wild” means for this CVE

For CVE-2023-20109, the practical meaning is simple: this is not a theoretical bug to track for later, it is a vulnerability CISA has already judged to be actively exploited. That moves the issue from ordinary vulnerability management into urgent exposure reduction, because confirmed exploitation means attackers have had a working path against real targets.

When a Cisco IOS or IOS XE edge system is in scope, the first question is whether it is reachable and whether the affected VPN feature is actually enabled on any device you operate. CISA’s Known Exploited Vulnerabilities Catalog is the authoritative source for confirming that the item is treated as actively exploited, while the vendor advisory should be used for exact product applicability and remediation steps.

Because the flaw is an out-of-bounds write in a remote-access edge component, treat it as an exposure on a high-value trust boundary rather than as a low-impact software defect. Edge VPN systems often sit in front of privileged access paths, so the question is not only whether the bug is exploitable, but whether successful exploitation would put credentials, sessions, or internal reachability at risk before defenders notice.

How to confirm exposure and prioritise response

Start by inventorying every Cisco IOS and IOS XE instance that could provide Group Encrypted Transport VPN service, then compare that list with the vendor’s affected-product guidance. If you do not know where the feature is enabled, assume you need to verify more than one configuration source, because edge appliances are often managed inconsistently across teams, sites, and change windows.

Prioritise devices that are Internet-facing, support administrative access, or bridge into sensitive internal networks. The most important operational judgement is that an exposed edge system with active remote access is usually a higher priority than a device that is technically vulnerable but isolated from untrusted traffic.

Use the CISA catalog entry as the trigger for urgency, but use the Cisco advisory for the exact fix path. NIST’s National Vulnerability Database can help with record-level reference data, but it should not be treated as the primary source for exploitation status or response timing.

Patch, mitigate, and look for compromise before and after remediation

If patching is available, apply it as soon as operationally possible. If a maintenance window must wait, use vendor-recommended mitigations immediately, reduce exposure to the smallest practical set of source networks, and remove any unnecessary remote management paths that widen blast radius.

Do not stop at fixing the software. Because CISA only lists vulnerabilities with confirmed exploitation, review logs for signs that the device was used before remediation, including unusual VPN activity, unexpected admin access, configuration changes, and any session or authentication anomalies around the period of exposure.

For a vulnerability in a remote-access edge device, the compromise check is often as important as the patch itself. If there is any evidence of successful exploitation, treat the device as a possible entry point into the broader environment and assess whether adjacent accounts, sessions, or credentials may need rotation or invalidation.

Risk and Threat Considerations

Actively exploited edge-device vulnerabilities are attractive because they can convert a single external flaw into internal reachability, persistence, or privileged access. In a VPN context, that can mean an attacker gains a foothold exactly where defenders are most likely to trust traffic and where normal access patterns are already dense.

Failure mechanism: An out-of-bounds write can allow memory corruption during processing of crafted traffic, which makes remote exploitation feasible when the vulnerable service is reachable. On an edge system, that failure can become a path to device compromise, session abuse, or follow-on internal access.

Impact: The immediate impact can range from service disruption to full device compromise, but the larger concern is trust boundary collapse. Once an externally reachable VPN device is compromised, attackers may be able to observe, pivot, or reuse access paths that were intended to protect the internal network.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

NIST SP 800-53 Rev 5, CIS Controls v8 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.

Framework	Control / Reference	Relevance
NIST SP 800-53 Rev 5	SI-2 — Flaw Remediation	CVE remediation and exposure reduction require timely flaw correction on affected edge systems.
	IR-4 — Incident Handling	Confirmed exploitation means teams should investigate for signs of compromise and contain affected devices.
Recommendation — Track, prioritize, and remediate the vulnerable Cisco edge software promptly. Investigate the device for compromise indicators and contain any suspected affected host.
CIS Controls v8	CIS-7 — Continuous Vulnerability Management	KEV-listed exploitation makes rapid identification and remediation of exposed systems materially necessary.
	CIS-16 — Application Software Security	Vendor remediation and secure configuration of exposed software are central to reducing this attack surface.
Recommendation — Scan for affected Cisco devices and accelerate remediation using exploit-aware prioritization. Apply vendor fixes and hardening guidance to the exposed VPN service.
NIST CSF 2.0	DE.CM-01 — Network Monitoring	Post-exploitation review depends on monitoring for unusual activity on exposed edge devices.
Recommendation — Monitor VPN and admin activity for anomalies after exposure is discovered.

Practitioner Guidance

What to verify: Confirm whether any Cisco IOS or IOS XE device in your estate is running the affected VPN feature and whether it is exposed to untrusted networks. If the answer is unclear, treat the device as high priority until you can prove otherwise.

Decision rule: If the device is Internet-facing or supports critical remote access, patch or mitigate before deferring to routine maintenance. If patching must wait, narrow exposure first, then collect evidence of prior compromise before returning the device to normal service.

What good looks like: A clean outcome means the vulnerable feature is either removed from exposure, patched, or mitigated, and the device has been checked for unusual access, configuration drift, or post-exploitation activity.

Practitioner takeaway: For a KEV-listed edge vulnerability, the right sequence is always exposure check, remediation, then compromise review, because active exploitation changes the question from “should we patch?” to “how far did the attacker get before we did?”

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NHIMG Editorial Note
Reviewed and updated by the NHIMG editorial team on October 18, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org