dbcve.org
iOSOperating system · Cisco

CVE-2009-2872

MEDIUM · 6.8 CVSS v2.0 Published 2009-09-28
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
74/100
Remediation priority · Elevated
Remotely reachable 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
Cisco IOS 12.0 through 12.4, when IP-based tunnels and the Cisco Express Forwarding feature are enabled, allows remote attackers to cause a denial of service (device reload) via a malformed packet that is not properly handled during switching from one tunnel to a second tunnel, aka Bug IDs CSCsh97579 and CSCsq31776.

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 denial of service vulnerability in Cisco IOS versions 12.0 through 12.4 where malformed packets processed during tunnel switching (when both IP-based tunnels and Cisco Express Forwarding are enabled) can cause the device to reload unexpectedly.

MitigationUpgrade to a patched Cisco IOS version or, as a workaround, disable either Cisco Express Forwarding (no CEF) or the IP-based tunnel interfaces if the upgrade cannot be performed immediately.

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:= 12.0= 12.0da= 12.0db= 12.0dc= 12.0s= 12.0sc= 12.0sl= 12.0sp= 12.0st= 12.0sx= 12.0sy= 12.0sz

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
Authentication
Single
Confidentiality
None
Integrity
None
Availability
Complete

AV:N/AC:L/Au:S/C:N/I:N/A:C

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 Cisco IOS version
    Execute 'show version' on the device CLI and locate the version string in the output (e.g., 'Cisco IOS Software, 12.0...')
    Affected if The version matches one of the affected 12.0 variants (12.0, 12.0da, 12.0db, 12.0dc, 12.0s, 12.0sc, 12.0sl, 12.0sp, 12.0st, 12.0sx, 12.0sy, 12.0sz) or falls within the 12.0 through 12.4 range mentioned in the advisory
  2. Verify if Cisco Express Forwarding is enabled
    Execute 'show cef summary' or 'show ip cef' and check if CEF is shown as enabled and operational
    Affected if CEF is enabled and running (output shows 'IP CEF with prefixes' and a table location count greater than zero)
  3. Identify if IP-based tunnel interfaces exist
    Execute 'show ip interface brief | include Tunnel' or 'show interface tunnel' to list all tunnel interfaces configured
    Affected if Any Tunnel interfaces with IP addresses assigned are present in the configuration

The device is affected if it runs a vulnerable IOS 12.0-12.4 version AND has both Cisco Express Forwarding enabled AND IP-based tunnel interfaces configured simultaneously.

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

Upgrade to a patched Cisco IOS version or, as a workaround, disable either Cisco Express Forwarding (no CEF) or the IP-based tunnel interfaces if the upgrade cannot be performed immediately.

Fix this in iOS Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,800
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,880.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2009-2872 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2009-2872 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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