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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 15 Apr 2022.
Ios XrOperating system · Cisco

CVE-2009-2055

MEDIUM · 5.9 CVSS v3.1 Published 2009-08-19
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
100/100
Remediation priority · Urgent
In the wild Remotely reachable No privileges Zero-click Patch available

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 XR 3.4.0 through 3.8.1 allows remote attackers to cause a denial of service (session reset) via a BGP UPDATE message with an invalid attribute, as demonstrated in the wild on 17 August 2009.

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

Cisco IOS XR versions 3.4.0 through 3.8.1 contains a vulnerability in the BGP (Border Gateway Protocol) implementation where specially crafted UPDATE messages with invalid attributes trigger a session reset, causing denial of service. The attacker exploits lack of proper input validation on BGP attribute handling.

MitigationUpgrade Cisco IOS XR to a version beyond 3.8.1 that contains the fix, or apply vendor-supplied patches if available. Implement BGP peer filtering and route validation as an interim compensating control.

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
Ios XrOperating system
Affected:= 3.4= 3.4.0= 3.4.1= 3.4.2= 3.4.3= 3.5= 3.5.2= 3.5.3= 3.5.4= 3.6.0= 3.6.1= 3.6.2

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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:H/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 XR version
    Execute 'show version' or 'admin show version' from the IOS XR CLI to retrieve the running software version
    Affected if The displayed version falls within 3.4.0 through 3.8.1 (or 3.4.x through 3.6.x based on the enumerated list)
  2. Confirm BGP is configured
    Execute 'show bgp summary' or 'show bgp vrf all summary' to check if BGP is running and has any neighbors configured
    Affected if BGP is active with at least one neighbor peer configured; the vulnerability only affects systems with BGP enabled
  3. Verify BGP neighbor status
    Execute 'show bgp neighbors' to list all BGP peer relationships and their current state
    Affected if Any BGP peers are established; the exploit targets active BGP sessions via crafted UPDATE messages
  4. Review BGP attribute handling logs
    Check system logs (using 'show logging' or review syslog/buffer) for BGP UPDATE messages or attribute-related errors
    Affected if Unexpected BGP resets or attribute validation errors appear in logs, which may indicate exploitation attempts

You are affected if the device runs Cisco IOS XR version 3.4.0 through 3.8.1 and has BGP enabled with configured peers.

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
Patch available Apply the vendor patch
Vendor patch www.cisco.com →
Interim mitigation

Upgrade Cisco IOS XR to a version beyond 3.8.1 that contains the fix, or apply vendor-supplied patches if available. Implement BGP peer filtering and route validation as an interim compensating control.

Recommended fix Moderate confidence

Cisco IOS XR 3.9.0 or later (or migrate to current IOS XR 7.x release if hardware supports it)

  1. 1. Identify all Cisco IOS XR devices currently running versions 3.4.0 through 3.8.1
  2. 2. Review the Cisco IOS XR software upgrade guide for your specific hardware platform
  3. 3. Plan maintenance window for upgrade - this will cause brief BGP session disruption
  4. 4. Download IOS XR software version 3.9.0 or later from Cisco Software Central (requires valid service contract)
  5. 5. Back up current running configuration and Cisco IOS XR software image
  6. 6. Install the new IOS XR image following Cisco's standard upgrade procedures
  7. 7. After upgrade, verify BGP sessions are established and stable
  8. 8. Monitor for any BGP session flaps or errors
Caveat Upgrading across major IOS XR releases (3.x to 4.x/5.x) may require configuration changes; verify hardware compatibility before upgrading to newer branches

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

Fix this in Ios Xr Exploited in the wild — priority engagement
  • 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-2009-2055 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