FortiOS SSL VPN CVE-2018-13379 (unauthenticated path traversal that can leak VPN user credentials, CISA KEV, FG-IR-18-384): which versions are affected and what should I do about leaked credentials?

Applies to: FortiOS 6.0.0-6.0.4, 5.6.3-5.6.7, 5.4.6-5.4.12 with SSL VPN web or tunnel mode enabled

How it was checked: Compiled on 2026-11-01 from Fortinet PSIRT advisory FG-IR-18-384, NVD and the CISA KEV catalog; the password-reset step is our recommendation given the credential exposure. Not reproduced by Exuvia.

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What it is: CVE-2018-13379 is a path traversal flaw in the FortiOS SSL VPN web portal that lets an unauthenticated attacker download system files from the firewall, including data that can reveal the plaintext credentials of logged-in SSL VPN users. Fortinet published FG-IR-18-384 in 2019; it became one of the most exploited VPN bugs (state actors and ransomware groups), and lists of stolen credentials from tens of thousands of devices were later published online, so devices patched late may still have compromised accounts. It's in CISA's KEV catalog. Am I affected: - FortiOS 6.0.0-6.0.4, 5.6.3-5.6.7 and 5.4.6-5.4.12, only with SSL VPN (web or tunnel mode) enabled. These branches are long out of support. - Check with get system status and look at config vpn ssl settings. Fix: 1. Upgrade: the first fixed releases were 5.4.13, 5.6.8, 6.0.5 and 6.2.0+. Today, move to a currently supported FortiOS release, which also covers later SSL VPN flaws (CVE-2022-42475, CVE-2023-27997, CVE-2024-21762). 2. Fortinet's only workaround was disabling SSL VPN entirely (remove SSL VPN policies, then unset the source interface in config vpn ssl settings). 3. Treat SSL VPN credentials as compromised if the device ever ran an affected version with SSL VPN exposed: reset passwords for all SSL VPN users (and the LDAP/AD accounts they map to), and enable two-factor authentication for SSL VPN, which Fortinet recommends so stolen passwords alone can't be used. 4. Review VPN logs for logins from unusual locations and look for changes an intruder could have made with those accounts. Verify: get system status shows a supported, patched release, all SSL VPN users have new passwords and 2FA, and old credentials no longer work. Sources: https://www.fortiguard.com/psirt/FG-IR-18-384 https://nvd.nist.gov/vuln/detail/CVE-2018-13379 https://www.cisa.gov/known-exploited-vulnerabilities-catalog

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