Cisco IOS Software Login Enhancements Remote Denial of Service Vulnerability (CVE-2018-0180)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco devices running Cisco IOS Software Release 15.4(2)T, 15.4(3)M, or 15.4(2)CG and later with Login Enhancements (Login Block) enabled
An unauthenticated, remote attacker can trigger an unexpected system reload, leading to a complete Denial of Service (DoS) condition
Apply the official Cisco IOS software updates, or temporarily disable the 'login block-for' feature and restrict virtual terminal (vty) access using infrastructure ACLs
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrade to a non-vulnerable Cisco IOS Software release as recommended by Cisco. Below is an example of upgrading the IOS image via TFTP:
# Download the secure IOS image from the TFTP server to flash memory
copy tftp: flash:
# Address or name of remote host? 192.168.1.100
# Source filename? c3900e-universalk9-mz.SPA.155-3.M.bin
# Destination filename [c3900e-universalk9-mz.SPA.155-3.M.bin]?
# Configure the system to boot from the new image
configure terminal
no boot system
boot system flash c3900e-universalk9-mz.SPA.155-3.M.bin
end
write memory2. Temporary Workaround & Hardening Configuration
If an immediate upgrade is not feasible, disable the vulnerable 'login block-for' configuration and restrict vty access to trusted management hosts only.
configure terminal
# Workaround: Disable the login block feature
no login block-for
# Hardening: Restrict SSH access to trusted management subnet (e.g., 10.1.1.0/24)
ip access-list standard MGMT_HOSTS
permit 10.1.1.0 0.0.0.255
deny any log
line vty 0 4
access-class MGMT_HOSTS in
transport input ssh
end
write memory3. Log Audit & IoC Verification Commands
Verify if the vulnerable feature is enabled and inspect system logs for unexpected reloads or login anomalies.
# Check if the login block feature is currently active
show running-config | include login block-for
# Inspect reload history and login-related logs
show version | include returned to ROM
show logging | include %SEC_LOGIN- or %SYS-5-RELOADStop 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-2018-0180) exists within the Login Enhancements (Login Block) feature of Cisco IOS Software. It is classified under resource management errors (CWE-399). The Login Block feature is designed to mitigate brute-force attacks by blocking login attempts for a specified duration. However, due to improper handling of specific login request sequences, the system fails to manage internal states correctly, leading to memory corruption or unhandled exceptions that trigger a device reload.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated remote attacker can exploit this vulnerability by targeting an open virtual terminal line (vty, such as SSH or Telnet) on an affected Cisco device where the Login Block feature is active. By sending crafted login attempts or specific authentication sequences, the attacker triggers a null pointer dereference or kernel panic within the IOS operating system. This causes the device to crash and reload, terminating all active network connections and routing services.
3. Infrastructure & Business Impact
This vulnerability is cataloged in CISA's Known Exploited Vulnerabilities (KEV) list, indicating active exploitation in the wild. Because a single unauthenticated packet sequence can force a core router or gateway to reload, this vulnerability poses a severe threat to network availability and business continuity, potentially causing widespread outages across enterprise infrastructures.
Official Vendor Advisories & References
Multiple vulnerabilities in the Login Enhancements (Login Block) feature of Cisco IOS Software could allow an unauthenticated, remote attacker to trigger a reload of an affected system, resulting in a denial of service (DoS) condition. These vulnerabilities affect Cisco devices that are running Cisco IOS Software Release 15.4(2)T, 15.4(3)M, or 15.4(2)CG and later. Cisco Bug IDs: CSCuy32360, CSCuz60599.
Frequently Asked SecOps Questions (CVE-2018-0180)
FAQQ1. How critical is CVE-2018-0180 and is it actively exploited in the wild?
CVE-2018-0180 is rated CVSS 5.9 (MEDIUM) with a 30-day EPSS exploitation probability of 4.9%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2018-0180?
Primary impacted vendors include cisco across ios. Scope summary: Cisco devices running Cisco IOS Software Release 15.4(2)T, 15.4(3)M, or 15.4(2)CG and later with the Login Block feature configured
Q3. What temporary mitigations or workarounds exist for CVE-2018-0180 before patching?
[Mitigation] Apply the official Cisco IOS software updates, or temporarily disable the 'login block-for' feature and restrict virtual terminal (vty) access using infrastructure ACLs Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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