Cisco IOS and IOS XE QoS Subsystem Remote Code Execution and DoS Vulnerability (CVE-2018-0151)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco IOS and IOS XE Software with the Quality of Service (QoS) subsystem enabled and listening on UDP port 18999.
An unauthenticated, remote attacker can execute arbitrary code with elevated privileges or cause a denial of service (DoS) condition via device reload.
Apply official Cisco software updates, or restrict access to UDP port 18999 using Infrastructure Access Control Lists (iACLs).
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Download and apply the recommended fixed release from the Cisco Software Center.
! Example: Downloading and configuring a secure IOS XE image via TFTP
copy tftp: flash:
Address or name of remote host? 192.168.1.100
Source filename? cat3k_caa-universalk9.SPA.03.E.bin
Destination filename [cat3k_caa-universalk9.SPA.03.E.bin]?
configure terminal
no boot system
boot system flash:cat3k_caa-universalk9.SPA.03.E.bin
end
write memory
reload2. Temporary Workaround & Hardening Configuration
If patching cannot be performed immediately, apply an Access Control List (ACL) to block incoming traffic to UDP port 18999.
! Define ACL to block UDP port 18999
configure terminal
ip access-list extended BLOCK_QOS_EXPLOIT
deny udp any any eq 18999
permit ip any any
exit
! Apply ACL to the external-facing interface
interface GigabitEthernet0/0
ip access-group BLOCK_QOS_EXPLOIT in
end
write memory3. Log Audit & IoC Verification Commands
Verify if the device is listening on UDP port 18999 and check for unexpected reload events in the system logs.
! Check for active UDP 18999 sockets and reload logs
show sockets | include 18999
show logging | include %SYS-2-RELOAD|%ALIGN-3-SPURIOUS
show version | include SoftwareStop 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 exists in the Quality of Service (QoS) subsystem of Cisco IOS and Cisco IOS XE Software. The root cause is improper bounds checking of specific values within packets destined for UDP port 18999 of an affected device. When these malformed packets are processed, an exploitable buffer overflow condition (CWE-119) occurs.
2. Exploitation Mechanics & Attack Scenario
An attacker can exploit this vulnerability by sending crafted UDP packets to UDP port 18999 of an affected device. Because the vulnerability is triggered during packet parsing by the QoS subsystem, no authentication is required. A successful exploit allows the attacker to overwrite memory structures, hijacking the execution flow to run arbitrary code with elevated privileges or causing the device to crash and reload, resulting in a temporary DoS. Note that transit traffic passing through the device does not trigger this vulnerability; the packets must target the device directly.
3. Infrastructure & Business Impact
Cisco IOS and IOS XE devices form the backbone of enterprise and service provider networks. With a CVSS score of 9.8 and its inclusion in the CISA KEV catalog, this vulnerability poses a severe threat. Successful exploitation could lead to complete compromise of the network infrastructure, enabling lateral movement, traffic interception, or widespread network outages.
Official Vendor Advisories & References
A vulnerability in the quality of service (QoS) subsystem of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition or execute arbitrary code with elevated privileges. The vulnerability is due to incorrect bounds checking of certain values in packets that are destined for UDP port 18999 of an affected device. An attacker could exploit this vulnerability by sending malicious packets to an affected device. When the packets are processed, an exploitable buffer overflow condition may occur. A successful exploit could allow the attacker to execute arbitrary code on the affected device with elevated privileges. The attacker could also leverage this vulnerability to cause the device to reload, causing a temporary DoS condition while the device is reloading. The malicious packets must be destined to and processed by an affected device. Traffic transiting a device will not trigger the vulnerability. Cisco Bug IDs: CSCvf73881.
Frequently Asked SecOps Questions (CVE-2018-0151)
FAQQ1. How critical is CVE-2018-0151 and is it actively exploited in the wild?
CVE-2018-0151 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 14.2%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2018-0151?
Primary impacted vendors include cisco across ios, ios_xe. Scope summary: All Cisco IOS and IOS XE Software versions where the QoS feature is active and UDP port 18999 is reachable (Cisco Bug ID: CSCvf73881).
Q3. What temporary mitigations or workarounds exist for CVE-2018-0151 before patching?
[Mitigation] Apply official Cisco software updates, or restrict access to UDP port 18999 using Infrastructure Access Control Lists (iACLs). Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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