Cisco IOS and IOS XE Software: code execution flaw under attack

What is affected

Cisco IOS and IOS XE Software is found on ordinary personal computers and phones, so this is not only a problem for companies. If you use it and have not updated since the fix was released, you are exposed.

The Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and IOS XE contains a vulnerability that could allow an authenticated, remote attacker to remotely execute code on an affected system or cause an affected system to reload.

What an attacker can do

This is a code execution flaw. It lets an attacker run their own commands or programs on the affected system. In practice that usually means taking it over: installing malware, stealing data or using it to reach other devices on the same network.

How it is reached

Over the internet or network

Access the attacker needs

A basic user account

Does the victim have to do something?

No, works without the victim doing anything

What to do

1. Update Cisco IOS and IOS XE Software now. Open the update or "About" screen, install whatever is offered and restart the app or device, because the fix is not active until you do.
2. Turn on automatic updates so the next fix arrives without you having to look for it.
3. If your device is too old to receive this update, stop using the affected app for anything sensitive and plan a replacement.

Apply updates per vendor instructions.

Vendor advisories and fixes

• sec.cloudapps.cisco.comsec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170629-sn

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on April 19, 2023, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by May 10, 2023, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 21% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 98% of all scored vulnerabilities.

Its CVSS severity score is 8.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

A vulnerability in the SNMP implementation of could allow an authenticated, remote attacker to cause a reload of the affected system or to remotely execute code. An attacker could exploit this vulnerability by sending a crafted SNMP packet to the affected device.  The vulnerability is due to a buffer overflow in the affected code area. The vulnerability affects all versions of SNMP (versions 1, 2c, and 3). The attacker must know the SNMP read only community string (SNMP version 2c or earlier) or the user credentials (SNMPv3). An exploit could allow the attacker to execute arbitrary code and obtain full control of the system or to cause a reload of the affected system. Only traffic directed to the affected system can be used to exploit this vulnerability.