CVE-2018-0173
Cisco IOS and IOS XE Software Improper Input Validation Vulnerability
Description
CVE-2018-0173 is a denial-of-service vulnerability in Cisco IOS and IOS XE Software. A vulnerability in the Cisco IOS Software and Cisco IOS XE Software function that restores encapsulated option 82 information in DHCP Version 4 (DHCPv4) packets can allow for denial-of-service (DoS). Successful exploitation could result in denial of service through system crashes on affected devices. CISA has added CVE-2018-0173 to the Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. The EPSS score of 4.07% (88.4th percentile) indicates a notable likelihood of exploitation activity.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| cisco | ios | denali-16.3.4; <= 15.2\(6\)e0a; <= 15.2\(4a\)ea5 |
| cisco | ios xe | denali-16.3.4; <= 15.2\(6\)e0a; <= 15.2\(4a\)ea5 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
References
- http://www.securityfocus.com/bid/103545(Broken Link, Third Party Advisory, VDB Entry)
- http://www.securitytracker.com/id/1040591(Broken Link, Third Party Advisory, VDB Entry)
- https://ics-cert.us-cert.gov/advisories/ICSA-18-107-04(Third Party Advisory, US Government Resource)
- https://ics-cert.us-cert.gov/advisories/ICSA-18-107-05(Third Party Advisory, US Government Resource)
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-dhcpr2(Vendor Advisory)
- https://www.tenable.com/security/research/tra-2018-06(Third Party Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2018-0173(US Government Resource)
Weakness Type
CWE-20: Improper Input Validation
Improper Input Validation is a software weakness where a product receives input or data but does not validate or incorrectly validates that the input has the properties required to process data safely and correctly. This vulnerability occurs when applications accept user-supplied data without verifying that it conforms to expected formats, lengths, types, or ranges.
Learn more: CWE-20 — Improper Input Validation
Impact Analysis
CVE-2018-0173 threatens the availability of Cisco IOS and IOS XE Software, as exploitation can cause denial-of-service conditions, resulting in service disruption. With a CVSS score of 8.6 (HIGH) and a network-based attack vector requiring no authentication, the barrier to exploitation is low. The changed scope indicates that exploitation can affect resources beyond the vulnerable component, potentially impacting downstream network services and connected systems. In enterprise environments, repeated exploitation could cause sustained network outages affecting business operations, communications, and service availability. Network infrastructure devices are high-value targets, and their unavailability can have cascading effects across the organization.
Exploit Maturity
CVE-2018-0173 is listed in the CISA Known Exploited Vulnerabilities catalog, confirming that this vulnerability has been exploited in real-world attacks. The EPSS score of 4.07% (88.4th percentile) indicates a significant probability of exploitation. Organizations should treat this vulnerability as an active and ongoing threat requiring immediate remediation.
Remediation
- Apply vendor updates immediately as required by CISA KEV: Apply updates per vendor instructions.
- If immediate patching is not possible, implement interim mitigations such as restricting access to the affected DHCP service to trusted networks only using access control lists.
- Monitor affected devices for signs of exploitation, including unexpected reloads, unusual network traffic, and anomalous process behavior.
- Ensure network monitoring and alerting is configured to detect denial-of-service conditions affecting the Cisco IOS and IOS XE Software infrastructure.
- Maintain up-to-date device configurations and backups to enable rapid recovery if exploitation causes device reloads.
Technical Details
CVE-2018-0173 is a denial-of-service vulnerability in the affected component of Cisco IOS and IOS XE Software. The vulnerability allows an unauthenticated remote attacker to cause a denial-of-service condition by sending specially crafted DHCP packets. The CVSS v3.1 score of 8.6 reflects low attack complexity, no required privileges, and high impact on availability. The changed scope in the CVSS vector indicates that exploitation can impact resources beyond the vulnerable component itself.
Frequently Asked Questions
Is CVE-2018-0173 being actively exploited?
Yes. CVE-2018-0173 is listed in the CISA Known Exploited Vulnerabilities catalog, confirming active exploitation. The EPSS score of 4.07% (88.4th percentile) further indicates a notable likelihood of ongoing exploitation.
What products are affected by CVE-2018-0173?
CVE-2018-0173 affects Cisco IOS and IOS XE Software. Specifically, affected products include Cisco Ios, Cisco Ios Xe.
How do I fix CVE-2018-0173?
Apply updates per vendor instructions. If immediate patching is not feasible, apply interim mitigations such as access control restrictions and enhanced monitoring to detect exploitation attempts.
How severe is CVE-2018-0173?
CVE-2018-0173 has a CVSS score of 8.6 (HIGH). This is a high-severity denial-of-service vulnerability that can disrupt network operations. While it does not enable code execution, the availability impact on critical network infrastructure makes timely remediation essential.
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