dbcve.org
iOSOperating system · Cisco

CVE-2024-20307

HIGH · 7.5 CVSS v3.1 Published 2024-03-27
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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 IKEv1 fragmentation code of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a heap overflow, resulting in an affected device reloading. This vulnerability exists because crafted, fragmented IKEv1 packets are not properly reassembled. An attacker could exploit this vulnerability by sending crafted UDP packets to an affected system. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition. Note: Only traffic that is directed to the affected system can be used to exploit this vulnerability. This vulnerability can be triggered by IPv4 and IPv6 traffic.

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 · moderate confidence

A heap overflow vulnerability exists in the IKEv1 fragmentation code of Cisco IOS and IOS XE Software. The vulnerability stems from improper reassembly of crafted, fragmented IKEv1 packets. An unauthenticated remote attacker can send specially crafted UDP packets (IPv4 or IPv6) to trigger the overflow, causing the affected device to reload and result in a denial of service.

MitigationApply the Cisco patch/software update for this vulnerability. If immediate patching is not possible, consider disabling IKEv1 if not required, or implement network filtering to limit IKE traffic to trusted sources.

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:= 15.1\(2\)sg8= 15.1\(2\)sy8= 15.1\(2\)sy9= 15.1\(2\)sy10= 15.1\(2\)sy11= 15.1\(2\)sy12= 15.1\(2\)sy13= 15.1\(2\)sy14= 15.1\(2\)sy15= 15.1\(2\)sy16= 15.2\(1\)sy3= 15.2\(1\)sy4
Ios XeOperating system
Affected:= 3.4.8sg= 3.7.4e= 3.7.5e= 3.8.2e= 3.8.3e= 3.8.4e= 3.8.5ae= 3.8.5e= 3.8.6e= 3.8.7e= 3.8.8e= 3.8.9e

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 device and software version
    Run 'show version' on the device console or via SNMP/remote access. Look for the IOS or IOS XE version number in the output.
    Affected if The displayed version matches any of the affected versions listed (15.1(2)sg8 through 15.2(1)sy4 for iOS, or 3.4.8sg through 3.8.9e for IOS XE).
  2. Check if IKEv1 is configured
    Run 'show running-config | include isakmp' or 'show crypto isakmp profile' to see active IKEv1 (ISAKMP) configuration.
    Affected if Any IKEv1 policy, profile, or transform-set is actively configured on the device.
  3. Verify IKEv1 is enabled on any interface
    Run 'show crypto isakmp sa' to display active IKEv1 security associations, or review interface configurations with 'show ip interface' and check for crypto map applied.
    Affected if IKEv1 security associations exist or crypto maps are bound to interfaces handling IKE traffic.
  4. Confirm UDP port 500 is accessible
    Check firewall or ACL configurations with 'show access-lists' and verify UDP port 500 (IKE) is permitted on external-facing interfaces.
    Affected if UDP port 500 traffic from untrusted sources is allowed into the device.

The device is affected if it runs a Cisco iOS or IOS XE version within the listed affected ranges AND has IKEv1 enabled and reachable via UDP port 500.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the Cisco patch/software update for this vulnerability. If immediate patching is not possible, consider disabling IKEv1 if not required, or implement network filtering to limit IKE traffic to trusted sources.

Fix this in iOS Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-2024-20307 in production — separate from our analysis above.

No notes yet

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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