CVE-2018-0172
CVE-2018-0172 is a security flaw in Cisco IOS and IOS XE Software, the operating system on Cisco’s routers and switches. Attackers can corrupt memory in Cisco IOS and IOS XE Software from anywhere, without logging in, which they use to take it over. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 3 Mar 2022.[1]
Cisco IOS and IOS XE Software is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Cisco has published a fix or advice.
Description
CISA calls it an improper input validation in Cisco IOS and IOS XE Software. In its words: “A vulnerability in the DHCP option 82 encapsulation functionality of Cisco IOS Software and Cisco IOS XE Software could allow for denial-of-service (DoS).”[1]
The CVE record adds: “A vulnerability in the DHCP option 82 encapsulation functionality of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. The vulnerability exists because the affected software performs incomplete input validation of option 82 information that it receives in DHCP Version 4 (DHCPv4) packets from DHCP relay agents. An attacker could exploit this vulnerability by sending a crafted DHCPv4 packet to an affected device. A successful exploit could allow the attacker to cause a heap overflow condition on the affected device, which will cause the device to reload and result in a DoS condition. Cisco Bug IDs: CSCvg62730.”[2]
The underlying weakness is improper input validation (CWE-20), in MITRE’s list of common software weaknesses.
It scores 8.6 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Cisco’s advisory has them[3]. CISA names the product as Cisco IOS and IOS XE Software.
Most families won’t have Cisco IOS and IOS XE Software; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Mar 2022, 1,436 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 17 Mar 2022 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 8%. That’s in the top 6% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Cisco has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Cisco IOS and IOS XE Software is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 17 Mar 2022 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 8.6.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 8%.[4] |
See also
Other Cisco IOS and IOS XE Software flaws
- CVE-2017-6742: SNMP remote code execution ·
- CVE-2018-0173: improper input validation ·
- CVE-2018-0151: IOS software and cisco IOS XE software quality of service remote code execution ·
- CVE-2017-6743: SNMP remote code execution ·
- CVE-2017-6740: SNMP remote code execution ·
- CVE-2017-6739: SNMP remote code execution ·
Other Cisco flaws
- CVE-2026-76418, Cisco Secure Firewall ASA Software and Cisco Secure FTD Software: unchecked return value to NULL pointer dereference ·
- CVE-2026-76519, Cisco Secure Email Gateway: relative path traversal ·
- CVE-2026-76504, Cisco Catalyst SD-WAN Manager: hex encoding ·
- CVE-2026-76460, Cisco Identity Services Engine: incorrect use of privileged APIs ·
- CVE-2026-76461, Cisco Secure Email Gateway: SQL injection ·
Other improper input validation flaws
- CVE-2026-93952, Arista VeloCloud Orchestrator: improper input validation ·
- CVE-2019-1068, Microsoft SQL Server: remote code execution ·
- CVE-2026-12569, PTC Windchill and FlexPLM: improper input validation ·
- CVE-2026-34910, Ubiquiti UniFi OS: improper input validation ·
- CVE-2026-6973, Ivanti Endpoint Manager Mobile (EPMM): improper input validation ·
Added the same day
- CVE-2022-20708, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
- CVE-2022-20703, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
- CVE-2022-20701, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
- CVE-2022-20700, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
- CVE-2022-20699, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
Every Cisco flaw on CISA’s list · Everything added in March 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Cisco IOS and IOS XE Software Improper Input Validation Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Mar 2022.
- ^ National Institute of Standards and Technology. “CVE-2018-0172 Detail”. National Vulnerability Database, published 28 Mar 2018.
- ^ Cisco. Advisories and fixes: tools.cisco.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.078, percentile 94.7, 31 Oct 2026.
- CVE Program. “CVE-2018-0172”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.