CVE-2023-20273: Cisco Cisco IOS XE Web UI

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

Yes, if you run Cisco Cisco IOS XE Web UI. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2023-10-23, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2023-10-27; treat that as the outer limit, not the target.
EPSS 93.0%, percentile 99.8: FIRST’s model estimates a 93.0% chance of exploitation activity in the next 30 days, higher than 99.8% of all scored CVEs (very high). EPSS is a probability, not a verdict.
Needs an account (high (admin)). Exposure depends on who can log in.
Editorial verdict: Act now. Cisco IOS XE Web UI Zero-Day Chain Implants Devices — If any IOS XE device has its HTTP or HTTPS server reachable from an untrusted network and is not on a fixed release, treat it as compromised until proven otherwise; devices with the web UI disabled were never exposed.

What it is

A vulnerability in the web UI feature of Cisco IOS XE Software could allow an authenticated, remote attacker to inject commands with the privileges of root. This vulnerability is due to insufficient input validation. An attacker could exploit this vulnerability by sending crafted input to the web UI. A successful exploit could allow the attacker to inject commands to the underlying operating system with root privileges.

CISA’s summary

Cisco IOS XE contains a command injection vulnerability in the web user interface. When chained with CVE-2023-20198, the attacker can leverage the new local user to elevate privilege to root and write the implant to the file system. Cisco identified CVE-2023-20273 as the vulnerability exploited to deploy the implant. CVE-2021-1435, previously associated with the exploitation events, is no longer believed to be related to this activity.

Weakness type: CWE-78.

Product: Cisco Cisco IOS XE Web UI · Assigned by: cisco · Published: 2023-10-24

Affected and fixed versions

Vendor	Product	Affected versions (per CVE record)
Cisco	Cisco IOS XE Software	16.1.1, 16.1.2, 16.1.3, 16.2.1, 16.2.2, 16.3.1, 16.3.2, 16.3.3, 16.3.1a, 16.3.4, 16.3.5, 16.3.5b

Severity scores

Scored by	CVSS	Score	Vector
cisco	3.1	7.2 High	`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H`

Attack vector: network (remotely reachable)
Attack complexity: low
Privileges required: high (admin)
User interaction: none
Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

CISA KEV: added 2023-10-23; federal due date 2023-10-27. Known ransomware use: Unknown.
CISA required action: Verify that instances of Cisco IOS XE Web UI are in compliance with BOD 23-02 and apply mitigations per vendor instructions. For affected products (Cisco IOS XE Web UI exposed to the internet or to untrusted networks), follow vendor instructions to determine if a system may have been compromised and immediately report positive findings to CISA.
CISA SSVC assessment: exploitation active, automatable no, technical impact total.
FIRST EPSS (model of 2026-10-21): 92.99% probability of exploitation activity in the next 30 days; percentile 99.8.

Timeline

2023-10-16 — erroneo.us brief: Cisco IOS XE Web UI Zero-Day Chain Implants Devices
2023-10-23 — Added to CISA’s Known Exploited Vulnerabilities catalog
2023-10-24 — CVE record published by cisco
2023-10-27 — CISA remediation deadline for US federal agencies
2025-10-21 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.