dbcve.org
iOSOperating system · Cisco

CVE-2024-20308

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 underflow, 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 denial of service (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 · high confidence

A heap underflow vulnerability exists in the IKEv1 fragmentation reassembly code of Cisco IOS and IOS XE Software. An unauthenticated remote attacker can exploit this by sending crafted fragmented UDP packets to the affected device, causing a denial of service via device reload.

MitigationApply the appropriate Cisco IOS/IOS XE software update when available. As a workaround, block or restrict UDP port 500 (IKE) traffic at network boundaries to prevent external attackers from reaching affected devices.

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:= 12.4\(22\)md= 12.4\(22\)md1= 12.4\(22\)md2= 12.4\(22\)mda= 12.4\(22\)mda1= 12.4\(22\)mda2= 12.4\(22\)mda3= 12.4\(22\)mda4= 12.4\(22\)mda5= 12.4\(22\)mda6= 12.4\(22\)t= 12.4\(22\)t1
Ios XeOperating system
Affected:= 3.3.0sg= 3.3.1sg= 3.3.2sg= 3.4.0sg= 3.4.1sg= 3.4.2sg= 3.4.3sg= 3.4.4sg= 3.4.5sg= 3.4.6sg= 3.4.7sg= 3.4.8sg

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 Cisco iOS or IOS XE version
    Run 'show version' on the device CLI and locate the version string in the output (for example, look for 'Version 12.4(22)md' or 'Version 3.3.0SG').
    Affected if The installed version exactly matches one of the listed affected versions in the CVE (12.4(22)md through 12.4(22)t1 for iOS, or 3.3.0sg through 3.4.8sg for IOS XE).
  2. Confirm IKEv1 is configured
    Run 'show crypto isakmp policy' or 'show running-config | include crypto isakmp' to check for active IKEv1 policies.
    Affected if Any IKEv1 policy is configured and active on the device, indicating the IKEv1 fragmentation code path is present.
  3. Verify IKEv1 SA existence
    Run 'show crypto isakmp sa' to display active IKEv1 Security Associations.
    Affected if Any IKEv1 SAs are established or in progress, meaning the device is processing IKEv1 packets including fragments.
  4. Check if UDP port 500 is accessible
    From an external perspective, verify whether UDP port 500 (IKE) is open and reachable on the device interface (for example, using 'show udp connections' or network scanning).
    Affected if UDP port 500 is exposed to untrusted networks, allowing external attackers to send crafted fragmented IKEv1 packets to the device.

A device is affected if it runs one of the exact listed iOS or IOS XE versions AND has IKEv1 configured with UDP port 500 reachable from untrusted networks.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the appropriate Cisco IOS/IOS XE software update when available. As a workaround, block or restrict UDP port 500 (IKE) traffic at network boundaries to prevent external attackers from reaching affected devices.

Recommended fix High confidence

Upgrade to the fixed Cisco IOS/IOS XE release specified in the Cisco security advisory for CVE-2024-20308 (consult sec.cloudapps.cisco.com for exact version numbers)

  1. 1. Identify the current Cisco IOS or IOS XE version on the affected device using 'show version' command
  2. 2. Access Cisco's official security advisory portal at sec.cloudapps.cisco.com to obtain the specific fixed release for this CVE
  3. 3. Download the appropriate fixed Cisco IOS or IOS XE software version for your hardware platform
  4. 4. Upload the new software image to the device using TFTP, FTP, or SCP
  5. 5. Configure boot system command to point to the new image
  6. 6. Reload the device with 'reload' command to apply the new software version
  7. 7. After reboot, verify the new version is running using 'show version' and confirm the vulnerability is remediated
Caveat Older IOS 12.4 and IOS XE 3.x SG releases may have reached end-of-life; ensure the replacement version is supported for your hardware platform

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

Fix this in iOS Scoped from the published advisory
  • Consultation6.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,880
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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-2024-20308 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