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iOSOperating system · Cisco

CVE-2024-20312

HIGH · 7.4 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 →
79/100
Remediation priority · High
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 Intermediate System-to-Intermediate System (IS-IS) protocol of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient input validation when parsing an ingress IS-IS packet. An attacker could exploit this vulnerability by sending a crafted IS-IS packet to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition. Note: The IS-IS protocol is a routing protocol. To exploit this vulnerability, an attacker must be Layer 2-adjacent to the affected device and have formed an adjacency.

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 Cisco IOS/IOS XE Software's IS-IS protocol implementation allows an adjacent, unauthenticated attacker who has formed an IS-IS adjacency to send a specially crafted IS-IS packet that triggers insufficient input validation, causing the affected device to reload and result in a denial of service.

MitigationApply the vendor patch from Cisco for this vulnerability; as a compensating control, disable IS-IS on untrusted Layer 2 ports or implement ACLs to filter IS-IS packets from untrusted adjacent devices until the patch can be applied.

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\(1\)ex= 15.1\(1\)sy= 15.1\(1\)sy1= 15.1\(1\)sy2= 15.1\(1\)sy3= 15.1\(1\)sy4= 15.1\(1\)sy5= 15.1\(1\)sy6= 15.1\(2\)sg= 15.1\(2\)sg1= 15.1\(2\)sg2= 15.1\(2\)sg3
Ios XeOperating system
Affected:= 3.2.0se= 3.2.1se= 3.2.2se= 3.2.3se= 3.3.0se= 3.3.0xo= 3.3.1se= 3.3.1xo= 3.3.2se= 3.3.2xo= 3.3.3se= 3.3.4se

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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/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 installed Cisco IOS or IOS XE version
    Run 'show version' on the device CLI and locate the version string in the output
    Affected if The displayed version matches any of the affected versions listed in the CVE (e.g., 15.1(1)sy, 15.1(2)sg, 3.2.0se through 3.3.4se, or 15.0(1)ex)
  2. Determine if IS-IS protocol is enabled
    Run 'show ip protocol summary' or 'show isis protocol' to check if IS-IS is configured and running on any interface
    Affected if IS-IS protocol appears as enabled or active in the output
  3. Check IS-IS adjacency status
    Run 'show isis adjacency' to see if any IS-IS neighbors are currently connected
    Affected if Any IS-IS adjacencies are formed with adjacent devices
  4. Verify IS-IS configuration on Layer 2 ports
    Run 'show running-config | include isis' and review interface configurations for IS-IS under Layer 2 interfaces (such as switch ports or trunk ports)
    Affected if IS-IS is enabled on Layer 2 access ports or ports that connect to untrusted network segments

The device is affected if it runs an affected Cisco IOS or IOS XE version, has IS-IS protocol enabled, and has IS-IS adjacencies formed on any interface, particularly Layer 2 ports where an adjacent attacker could send malicious IS-IS packets.

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 vendor patch from Cisco for this vulnerability; as a compensating control, disable IS-IS on untrusted Layer 2 ports or implement ACLs to filter IS-IS packets from untrusted adjacent devices until the patch can be applied.

Fix this in iOS Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing6.0 h
  • Review / QA3.0 h
27.0 hours of engineering $4,800
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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-2024-20312 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