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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 24 Mar 2022.
iOSOperating system · Cisco

CVE-2017-12237

HIGH · 7.5 CVSS v3.1 Published 2017-09-29
Fix available
A fix is available. Upgrade to after 16.5 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability in the Internet Key Exchange Version 2 (IKEv2) module of Cisco IOS 15.0 through 15.6 and Cisco IOS XE 3.5 through 16.5 could allow an unauthenticated, remote attacker to cause high CPU utilization, traceback messages, or a reload of an affected device that leads to a denial of service (DoS) condition. The vulnerability is due to how an affected device processes certain IKEv2 packets. An attacker could exploit this vulnerability by sending specific IKEv2 packets to an affected device to be processed. A successful exploit could allow the attacker to cause high CPU utilization, traceback messages, or a reload of the affected device that leads to a DoS condition. This vulnerability affects Cisco devices that have the Internet Security Association and Key Management Protocol (ISAKMP) enabled. Although only IKEv2 packets can be used to trigger this vulnerability, devices that are running Cisco IOS Software or Cisco IOS XE Software are vulnerable when ISAKMP is enabled. A device does not need to be configured with any IKEv2-specific features to be vulnerable. Many features use IKEv2, including different types of VPNs such as the following: LAN-to-LAN VPN; Remote-access VPN, excluding SSL VPN; Dynamic Multipoint VPN (DMVPN); and FlexVPN. Cisco Bug IDs: CSCvc41277.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A vulnerability in the IKEv2 packet processing module of Cisco IOS 15.0-15.6 and IOS XE 3.5-16.5 allows unauthenticated remote attackers to cause high CPU utilization, traceback messages, or device reload by sending specific crafted IKEv2 packets to an affected device with ISAKMP enabled.

MitigationApply Cisco vendor patches for affected IOS/IOS XE versions. If patching is not immediately feasible, evaluate disabling ISAKMP/IKEv2 features if not required, or implement network-level filtering to limit IKEv2 packet exposure.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
iOSOperating system
Affected:>= 15.0, <= 15.6
Ios XeOperating system
Affected:>= 3.5.0e, <= 16.5

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the IOS or IOS XE version
    Run 'show version' on the device CLI and locate the version string in the output (e.g., 'Version 15.2(4)E' for IOS or 'Version 16.3.2' for IOS XE)
    Affected if The version falls within 15.0 to 15.6 for IOS, or between 3.5.0e and 16.5 for IOS XE
  2. Confirm the software type
    Run 'show version' and verify whether the device runs classic IOS or IOS XE (IOS XE typically shows 'IOS XE Software' in the output)
    Affected if The device runs IOS (not IOS XE) and the version is 15.0-15.6, or runs IOS XE with version 3.5.0e-16.5
  3. Check if ISAKMP is enabled
    Run 'show running-config | include isakmp' or 'show crypto isakmp' to see if ISAKMP is configured and active on any interface
    Affected if ISAKMP is enabled (any output showing 'isakmp enable' or active IKEv2/ISAKMP policies exists)
  4. Verify IKEv2 protocol processing is active
    Run 'show crypto ikev2 session' or check for IKEv2-related processes in 'show processes cpu history' to confirm the IKEv2 module is running
    Affected if IKEv2 sessions exist or the IKEv2 module is actively processing (even with default/minimal configuration)

A device is affected if it runs IOS 15.0-15.6 or IOS XE 3.5.0e-16.5 AND has ISAKMP enabled, regardless of whether explicit IKEv2 policies are configured.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 16.5
Interim mitigation

Apply Cisco vendor patches for affected IOS/IOS XE versions. If patching is not immediately feasible, evaluate disabling ISAKMP/IKEv2 features if not required, or implement network-level filtering to limit IKEv2 packet exposure.

Recommended fix Moderate confidence

Cisco IOS 15.7+ or Cisco IOS XE 16.6+ (latest stable release in the respective train)

  1. 1. Identify the current Cisco IOS or IOS XE version running on the affected device using 'show version' command.
  2. 2. Confirm ISAKMP is enabled on the device using 'show crypto isakmp sa' or 'show ip interface' to check for ISAKMP ports (UDP 500, 4500).
  3. 3. Schedule a maintenance window for the upgrade, as the device will require a reload.
  4. 4. Backup the current device configuration using 'copy running-config startup-config' or 'copy running-config tftp'.
  5. 5. Download the fixed Cisco IOS or IOS XE release from Cisco's download portal (software.cisco.com). For IOS 15.x, use 15.7 or later. For IOS XE, use 16.6 or later.
  6. 6. Upgrade the device using 'archive download-sw' or the appropriate method for your platform.
  7. 7. After upgrade, reload the device and verify the new version using 'show version'.
  8. 8. Verify the device is functioning normally and ISAKMP/IKEv2 is operational using 'show crypto isakmp sa'.
Caveat Review Cisco release notes for any configuration changes or deprecated features between your current version and the target version; some VPN configurations may need adjustment after upgrade.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in iOS Exploited in the wild — priority engagement
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  • Implementation2.0 h
  • Testing8.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,900
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2017-12237 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data