WatchGuard Firebox: vulnerability flaw under attack

What is affected

WatchGuard Firebox 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.

WatchGuard Fireware OS iked process contains an out of bounds write vulnerability in the OS iked process. This vulnerability may allow a remote unauthenticated attacker to execute arbitrary code and affects both the mobile user VPN with IKEv2 and the branch office VPN using IKEv2 when configured with a dynamic gateway peer.

What an attacker can do

This is a vulnerability flaw. It lets an attacker misuse the product in a way its maker did not intend. CISA lists it because attackers are confirmed to be using it against real systems.

How it is reached

Over the internet or network

Access the attacker needs

No account needed

Does the victim have to do something?

No, works without the victim doing anything

CISA records this vulnerability as known to be used in ransomware campaigns: attackers use it to get in, then encrypt files and demand payment.

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 WatchGuard Firebox 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 mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Vendor advisories and fixes

• watchguard.comwww.watchguard.com/wgrd-psirt/advisory/wgsa-2025-00027

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on December 19, 2025, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by December 26, 2025, 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 27% 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 9.3 out of 10 (critical), as recorded in the US National Vulnerability Database.

Technical description

An Out-of-bounds Write vulnerability in the WatchGuard Fireware OS iked process may allow a remote unauthenticated attacker to execute arbitrary code. This vulnerability affects both the mobile user VPN with IKEv2 and the branch office VPN using IKEv2 when configured with a dynamic gateway peer. If the Firebox was previously configured with the mobile user VPN with IKEv2 or a branch office VPN using IKEv2 to a dynamic gateway peer, and both of those configurations have since been deleted, that Firebox may still be vulnerable if a branch office VPN to a static gateway peer is still configured.