CVE-2022-20623 Overview
A vulnerability in the rate limiter for Bidirectional Forwarding Detection (BFD) traffic of Cisco NX-OS Software for Cisco Nexus 9000 Series Switches could allow an unauthenticated, remote attacker to cause BFD traffic to be dropped on an affected device. This vulnerability is due to a logic error in the BFD rate limiter functionality. An attacker could exploit this vulnerability by sending a crafted stream of traffic through the device. A successful exploit could allow the attacker to cause BFD traffic to be dropped, resulting in BFD session flaps that can cause route instability and dropped traffic, resulting in a denial of service (DoS) condition. This vulnerability applies to both IPv4 and IPv6 traffic.
Critical Impact
Successful exploitation leads to BFD session flaps causing network route instability and traffic drops, resulting in denial of service conditions affecting network availability.
Affected Products
- Cisco NX-OS Software
- Cisco Nexus 9000 Series Switches (N9K-C92160YC-X, N9K-C92300YC, N9K-C92304QC, N9K-C9232C, N9K-C92348GC-X)
- Cisco Nexus 9000 Series Line Cards (N9K-X97160YC-EX, N9K-X97284YC-FX, N9K-X9732C-EX, N9K-X9732C-FX, N9K-X9736C-EX, N9K-X9736C-FX, N9K-X9788TC-FX)
Discovery Timeline
- February 23, 2022 - CVE-2022-20623 published to NVD
- November 21, 2024 - Last updated in NVD database
Technical Details for CVE-2022-20623
Vulnerability Analysis
This denial of service vulnerability affects the Bidirectional Forwarding Detection (BFD) protocol implementation within Cisco NX-OS Software running on Nexus 9000 Series Switches. BFD is a critical network protocol used for rapid detection of communication failures between adjacent forwarding engines, enabling faster network convergence compared to traditional routing protocol timers.
The vulnerability exists in the rate limiter component responsible for managing BFD traffic flow. When the rate limiter processes incoming traffic, a logic error causes legitimate BFD control packets to be incorrectly dropped under certain conditions. This behavior is particularly concerning because BFD sessions are designed to detect failures quickly—typically within milliseconds—meaning any disruption to BFD traffic has immediate cascading effects on network stability.
An unauthenticated attacker positioned on the network can exploit this vulnerability by sending specially crafted traffic streams through the affected device. The attack does not require any privileges or user interaction, making it highly accessible to threat actors with network access.
Root Cause
The root cause is a logic error in the BFD rate limiter functionality within Cisco NX-OS Software. The rate limiter, designed to protect the control plane from excessive traffic, contains flawed logic that incorrectly classifies or handles certain traffic patterns. This causes the rate limiter to drop legitimate BFD packets when processing crafted traffic streams, rather than only limiting malicious or excessive traffic as intended.
Attack Vector
The attack vector is network-based and does not require authentication. An attacker can exploit this vulnerability remotely by sending a crafted stream of traffic through a vulnerable Cisco Nexus 9000 Series Switch. The attack triggers the logic error in the BFD rate limiter, causing:
- BFD control packets to be dropped
- BFD sessions to flap (transition between up and down states)
- Routing protocols to react to the perceived link failures
- Route instability and traffic blackholing across the affected network segment
The vulnerability affects both IPv4 and IPv6 traffic, expanding the attack surface across dual-stack network environments. Since BFD is often used in conjunction with routing protocols like OSPF, BGP, and IS-IS to provide fast failure detection, disrupting BFD can cause widespread network instability beyond the immediately targeted device.
Detection Methods for CVE-2022-20623
Indicators of Compromise
- Unexpected BFD session flaps logged on Cisco Nexus 9000 Series Switches without corresponding physical link failures
- Increased rate of BFD packet drops visible in control plane policer statistics
- Routing protocol adjacency flaps correlating with BFD session instability
- Anomalous traffic patterns or high volumes of traffic targeting BFD-enabled interfaces
Detection Strategies
- Monitor system logs for BFD session state changes using show bfd neighbors history command output
- Implement SNMP traps for BFD session state changes (ciscoBfdSessStateChange) to enable real-time alerting
- Configure NetFlow or sFlow to analyze traffic patterns and identify potential crafted traffic streams targeting affected devices
- Use Cisco NX-OS show system internal bfd event-history to review BFD subsystem events for anomalies
Monitoring Recommendations
- Establish baseline metrics for BFD session stability and alert on deviations exceeding normal operational variance
- Correlate BFD flap events with traffic analysis data to identify potential attack traffic sources
- Monitor control plane CPU utilization on Nexus 9000 switches, as DoS attacks may cause elevated processing load
- Implement centralized logging with SIEM integration to detect patterns of BFD instability across multiple devices
How to Mitigate CVE-2022-20623
Immediate Actions Required
- Review the Cisco Security Advisory on BFD DoS to determine if your NX-OS version is affected
- Inventory all Cisco Nexus 9000 Series Switches and line cards in your environment against the affected product list
- Plan and schedule NX-OS software upgrades to a fixed release during the next available maintenance window
- Implement network access controls to limit exposure of affected devices to untrusted traffic sources
Patch Information
Cisco has released software updates that address this vulnerability. Affected organizations should upgrade to a fixed NX-OS software release as specified in the official security advisory. Consult the Cisco Security Advisory on BFD DoS for specific fixed software versions and upgrade guidance applicable to your device model and current software release.
Workarounds
- There are no documented workarounds that fully address this vulnerability; software upgrade is the recommended remediation
- Implement access control lists (ACLs) to restrict traffic sources that can reach affected devices where operationally feasible
- Consider network segmentation to limit the blast radius of potential exploitation
- Monitor affected devices closely for signs of exploitation while planning upgrade activities
# Verify current NX-OS version on affected devices
show version
# Check BFD session status for monitoring
show bfd neighbors
# Review BFD configuration
show running-config bfd
# Monitor control plane policer statistics for dropped packets
show system internal access-list input entries details
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
