CVE-2023-20198
CVE-2023-20198 is a security flaw in Cisco IOS XE Web UI, the operating system on Cisco’s routers and switches. Attackers can use Cisco IOS XE Web UI to take full control of the machine from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 16 Oct 2023.[1]
Cisco IOS XE Web UI 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 a privilege escalation in Cisco IOS XE Web UI. In its words: “Cisco IOS XE Web UI contains a privilege escalation vulnerability in the web user interface that could allow a remote, unauthenticated attacker to create an account with privilege level 15 access. The attacker can then use that account to gain control of the affected device.”[1]
The CVE record adds: “Cisco is providing an update for the ongoing investigation into observed exploitation of the web UI feature in Cisco IOS XE Software. We are updating the list of fixed releases and adding the Software Checker. Our investigation has determined that the actors exploited two previously unknown issues. The attacker first exploited CVE-2023-20198 to gain initial access and issued a privilege 15 command to create a local user and password combination. This allowed the user to log in with normal user access. The attacker then exploited another component of the web UI feature, leveraging the new local user to elevate privilege to root and write the implant to the file system. Cisco has assigned CVE-2023-20273 to this issue. CVE-2023-20198 has been assigned a CVSS Score of 10.0. CVE-2023-20273 has been assigned a CVSS Score of 7.2. Both of these CVEs are being tracked by CSCwh87343.”[2]
The underlying weakness is CWE-420, in MITRE’s list of common software weaknesses.
It scores 10.0 out of 10 on the Common Vulnerability Scoring System, which rates it critical, 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 XE Web UI.
Most families won’t have Cisco IOS XE Web UI; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 16 Oct 2023, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 20 Oct 2023 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 over 99%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Cisco has published a fix or advice.[3] CISA’s required action: “Verify that instances of Cisco IOS XE Web UI are in compliance with BOD 23-02 and apply mitigations per vendor instructions.”[1]
- Check whether you use it.Cisco IOS XE Web UI 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 20 Oct 2023 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 10.0.[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 over 99%.[4] |
See also
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 ·
Similar flaws
- CVE-2025-54309, CrushFTP: unprotected alternate channel ·
Every Cisco flaw on CISA’s list · Everything added in October 2023
References
- ^ Cybersecurity and Infrastructure Security Agency. “Cisco IOS XE Web UI Privilege Escalation Vulnerability”. Known Exploited Vulnerabilities Catalog, added 16 Oct 2023.
- ^ National Institute of Standards and Technology. “CVE-2023-20198 Detail”. National Vulnerability Database, published 16 Oct 2023.
- ^ Cisco. Advisories and fixes: cisco.com, sec.cloudapps.cisco.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.996, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2023-20198”. 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.