Cisco IOS Software Login Enhancements Remote Denial of Service Vulnerability (CVE-2018-0179)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco devices running Cisco IOS Software Releases 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 persistent Denial of Service (DoS) condition
Upgrade to the latest patched Cisco IOS software release or temporarily disable/modify the Login Block configuration
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Download the patched Cisco IOS image from the Cisco Software Center and upgrade the device. Below is an example of upgrading the IOS image via TFTP.
# Enter privileged EXEC mode
enable
# Verify and backup current flash memory
show flash:
copy flash:cisco_ios_old.bin tftp://192.168.1.100/cisco_ios_old.bin
# Download the patched IOS image
copy tftp://192.168.1.100/cisco_ios_patched.bin flash:cisco_ios_patched.bin
# Configure boot system to use the new image
configure terminal
no boot system
boot system flash:cisco_ios_patched.bin
end
write memory
reload2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, disable the Login Block feature or restrict access to the VTY lines using an Access Control List (ACL).
configure terminal
# Workaround: Disable the Login Block feature
no login block-for
# Hardening: Restrict VTY access to trusted management subnets (e.g., 10.1.1.0/24)
ip access-list standard MGMT_ACL
permit 10.1.1.0 0.0.0.255
deny any log
line vty 0 4
access-class MGMT_ACL in
end
write memory3. Log Audit & IoC Verification Commands
Use the following commands to check the current IOS version, verify if Login Block is active, and inspect reload logs for potential exploitation attempts.
# 1. Check the running IOS version
show version | include Software
# 2. Check if Login Block is enabled
show running-config | include login block-for
# 3. Inspect reload history and system error logs
show version | include returned to ROM
show logging | include %SYS-5-RELOAD|%SYSTEM-3-ERRStop 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-2018-0179) exists in the Login Enhancements (commonly known as Login Block) feature of Cisco IOS Software. The Login Block feature is designed to mitigate brute-force attacks by blocking login attempts after consecutive failures. However, due to improper resource management (CWE-399) during the processing of specific login requests, the system fails to handle exceptions correctly, resulting in a kernel-level crash.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated remote attacker scans for Cisco devices with exposed management interfaces (such as VTY lines) where the Login Block feature is active. The attacker then transmits specially crafted login packets or generates a high volume of anomalous connection requests designed to trigger the login block mechanism. Because the internal login management process fails to handle these inputs gracefully, it triggers a system crash and forces the device to reload.
3. Infrastructure & Business Impact
This vulnerability is cataloged in CISA's Known Exploited Vulnerabilities (KEV), indicating active exploitation in the wild. If a core router or enterprise gateway is targeted, the resulting unexpected reload can disrupt routing paths, sever network connectivity, and cause severe operational downtime across the entire enterprise infrastructure.
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-2018-0179)
FAQQ1. How critical is CVE-2018-0179 and is it actively exploited in the wild?
CVE-2018-0179 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-2018-0179?
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 Login Block enabled
Q3. What temporary mitigations or workarounds exist for CVE-2018-0179 before patching?
[Mitigation] Upgrade to the latest patched Cisco IOS software release or temporarily disable/modify the Login Block configuration Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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