CVE-2025-20192: Cisco IOS XE IKEv1 DoS Vulnerability

CVE-2025-20192 Overview

CVE-2025-20192 is a denial of service (DoS) vulnerability in the Internet Key Exchange version 1 (IKEv1) implementation of Cisco IOS XE Software. An authenticated remote attacker with valid IKEv1 VPN credentials can send crafted IKEv1 messages to force the affected device to reload. The flaw resides in how IKEv1 phase 2 parameters are validated before being passed to the hardware cryptographic accelerator for IPsec security association creation. Successful exploitation disrupts network connectivity by triggering an unexpected device restart. The vulnerability is tracked under [CWE-232] (improper handling of undefined values).

Critical Impact

An authenticated attacker holding valid IKEv1 VPN credentials can remotely reload a Cisco IOS XE device, interrupting VPN services and all traffic transiting the appliance.

Affected Products

• Cisco IOS XE Software with IKEv1 VPN functionality enabled
• Cisco devices using a hardware cryptographic accelerator for IPsec
• Refer to the Cisco Security Advisory for the full list of affected releases

Discovery Timeline

• 2025-05-07 - CVE-2025-20192 published to the National Vulnerability Database (NVD)
• 2026-04-15 - Last updated in the NVD database

Technical Details for CVE-2025-20192

Vulnerability Analysis

The vulnerability exists in the IKEv1 implementation used to negotiate IPsec security associations on Cisco IOS XE Software. The IKEv1 protocol performs two phases of negotiation. Phase 1 establishes a secure channel between peers, and phase 2 negotiates the parameters for the IPsec tunnel itself. CVE-2025-20192 affects phase 2 processing.

When an authenticated peer submits IKEv1 phase 2 parameters, the affected code path hands the IPsec security association creation request to the hardware cryptographic accelerator without first validating all phase 2 parameter values. Undefined or malformed parameters reach the accelerator and trigger a fatal condition that reloads the device. The flaw is categorized as a denial of service issue rooted in improper handling of undefined values, mapped to [CWE-232].

Root Cause

The root cause is missing input validation on IKEv1 phase 2 parameters before the IPsec security association request is dispatched to the cryptographic hardware. Software-layer checks fail to reject crafted or out-of-spec parameter values. The accelerator then encounters values it cannot process safely, causing a crash of the device control plane.

Attack Vector

The attack vector is the network. An attacker must first authenticate as a valid IKEv1 VPN user, which limits the exploit pool to insiders or attackers who have obtained credentials through phishing, credential reuse, or prior compromise. After establishing IKEv1 phase 1, the attacker initiates phase 2 negotiation with crafted parameters that bypass software validation and reach the hardware crypto path. A single successful exploit attempt causes a device reload, disrupting VPN tunnels and any traffic routed through the affected device.

No public proof-of-concept exploit is currently available, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog. See the Cisco Security Advisory for technical details specific to affected releases.

Detection Methods for CVE-2025-20192

Indicators of Compromise

• Unexpected reloads of Cisco IOS XE devices coinciding with active IKEv1 phase 2 negotiations
• Crash files or core dumps referencing IPsec security association creation or the hardware crypto driver
• Repeated IKEv1 phase 2 negotiation attempts from a single authenticated peer immediately before a reload

Detection Strategies

• Correlate syslog %LINK and %SYS-5-RESTART reload events with preceding %CRYPTO- and %IKE- log entries from the same source peer
• Inspect IKEv1 phase 2 (Quick Mode) traffic for malformed proposals or unusual transform attributes from authenticated VPN users
• Track per-user IKEv1 session counts and flag accounts initiating abnormal volumes of phase 2 negotiations

Monitoring Recommendations

• Forward Cisco IOS XE syslog and crash telemetry to a centralized SIEM for retention and correlation
• Alert on any IOS XE device reload event in production VPN concentrators and investigate the preceding 5 minutes of IKE traffic
• Audit IKEv1 credential usage and rotate credentials for accounts that exhibit suspicious negotiation patterns

How to Mitigate CVE-2025-20192

Immediate Actions Required

• Apply the fixed Cisco IOS XE Software release identified in the Cisco Security Advisory
• Rotate IKEv1 VPN credentials and review accounts with VPN access for least-privilege compliance
• Restrict IKEv1 peer connectivity to known source addresses using infrastructure access control lists

Patch Information

Cisco has published a security advisory with fixed software versions. Administrators should consult the Cisco Security Advisory and upgrade affected devices to a release that contains the validation fix for IKEv1 phase 2 parameter handling.

Workarounds

• Where operationally feasible, migrate VPN tunnels from IKEv1 to IKEv2, which is not affected by this issue
• Apply control-plane policing (CoPP) and infrastructure ACLs to limit IKE traffic to trusted peer addresses
• Disable IKEv1 on devices that do not require legacy VPN connectivity

# Example: restrict IKE (UDP 500/4500) to known peer addresses
ip access-list extended IKE-PEERS
 permit udp host <trusted-peer-ip> any eq isakmp
 permit udp host <trusted-peer-ip> any eq non500-isakmp
 deny   udp any any eq isakmp
 deny   udp any any eq non500-isakmp
 permit ip any any
!
interface <wan-interface>
 ip access-group IKE-PEERS in