Cisco Adaptive Security Appliance (ASA): code execution flaw under attack

What is affected

Cisco Adaptive Security Appliance (ASA) is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

A vulnerability in the command-line interface (CLI) parser of Cisco ASA software could allow an authenticated, local attacker to create a denial-of-service (DoS) condition or potentially execute code.

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

Needs access to the device or a file opened on it

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. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
2. If you administer Cisco Adaptive Security Appliance (ASA) at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply updates per vendor instructions.

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on May 24, 2022, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by June 14, 2022, 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 23% 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 7.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

Cisco Adaptive Security Appliance (ASA) Software before 8.4(1) on ASA 5500, ASA 5500-X, PIX, and FWSM devices allows local users to gain privileges via invalid CLI commands, aka Bug ID CSCtu74257 or EPICBANANA.