Cisco IOS XR BGP UPDATE Attribute Validation Denial of Service Vulnerability (CVE-2009-2055)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco IOS XR Software versions 3.4.0 through 3.8.1 running on routing platforms
Remote attackers can trigger a denial of service (BGP session reset) by sending a crafted BGP UPDATE message with an invalid attribute, leading to routing instability
Apply official Cisco software patches or implement infrastructure ACLs and BGP TTL Security to restrict unauthorized BGP peer connections
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrade to a fixed Cisco IOS XR release or apply the appropriate Software Maintenance Upgrade (SMU) provided by Cisco. Use the following commands to verify and install updates:
# Verify current active software and SMUs
show install active
# Add and activate the fixed software image or SMU
admin
install add tftp://10.1.1.10/disk0/asr9k-p-3.8.2.smu.tar activate
install commit2. Temporary Workaround & Hardening Configuration
If patching cannot be performed immediately, secure the BGP control plane by implementing Infrastructure Access Control Lists (iACLs) and enabling BGP TTL Security (GTSM) to drop unauthorized or spoofed BGP packets.
# Configure Infrastructure ACL to restrict BGP access
ipv4 access-list ACL-BGP-PROTECT
permit tcp host 192.168.10.1 host 192.168.10.2 eq bgp
permit tcp host 192.168.10.1 eq bgp host 192.168.10.2
deny tcp any any eq bgp
!
interface GigabitEthernet0/0/0/0
ipv4 access-group ACL-BGP-PROTECT in
!
# Enable BGP TTL Security (GTSM)
router bgp 65001
neighbor 192.168.10.1
remote-as 65002
ttl-security
!3. Log Audit & IoC Verification Commands
Monitor the router logs for unexpected BGP session resets and notification messages associated with malformed attributes.
# Check BGP neighbor status and reset reasons
show bgp neighbors | include 'Reset|Notification|State'
# Search system logs for BGP notification errors
show logging | include 'BGP-3-NOTIFICATION'Stop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2009-2055) is an input validation issue (CWE-20) within the Border Gateway Protocol (BGP) implementation of Cisco IOS XR Software. The root cause lies in the improper handling and parsing of malformed or invalid attributes contained within incoming BGP UPDATE messages. Instead of gracefully ignoring or handling the invalid attribute, the BGP process terminates the affected peering session.
2. Exploitation Mechanics & Attack Scenario
An attacker capable of sending BGP traffic to an affected router can transmit a specially crafted BGP UPDATE packet containing an invalid attribute. When the vulnerable Cisco IOS XR device processes this packet, it encounters an unhandled exception in its BGP state machine, resulting in a session reset (sending a BGP Notification and tearing down the TCP connection). This can be executed by an established peer or via spoofed packets if proper path validation is not enforced.
3. Infrastructure & Business Impact
Because BGP is the backbone routing protocol for service providers and large enterprises, repeated session resets (route flapping) can cause severe routing instability. This leads to packet loss, increased latency, and potential routing blackholes, resulting in a significant disruption of network availability and business operations.
Official Vendor Advisories & References
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.
Frequently Asked SecOps Questions (CVE-2009-2055)
FAQQ1. How critical is CVE-2009-2055 and is it actively exploited in the wild?
CVE-2009-2055 is rated CVSS 5.9 (MEDIUM) with a 30-day EPSS exploitation probability of 3.3%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2009-2055?
Primary impacted vendors include cisco across ios_xr. Scope summary: Cisco IOS XR Software versions 3.4.0, 3.4.1, 3.4.2, 3.4.3, 3.5.0, 3.6.0, 3.6.1, 3.6.2, 3.7.0, 3.7.1, 3.7.2, 3.8.0, and 3.8.1
Q3. What temporary mitigations or workarounds exist for CVE-2009-2055 before patching?
[Mitigation] Apply official Cisco software patches or implement infrastructure ACLs and BGP TTL Security to restrict unauthorized BGP peer connections Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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