CVE-2018-13383 Fortinet FortiOS and FortiProxy Out-of-bounds Write
A heap buffer overflow in Fortinet FortiOS and FortiProxy may cause the SSL VPN web service termination for logged in users.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 10 Jan 2022.
- CISA lists it as known to be used in ransomware campaigns.
- Rated Medium severity (CVSS 4.3, scored by Vendor).
- This product type is often exposed to the internet, which is where attackers scan for it first.
- It has been in the catalogue for 1,761 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
A heap buffer overflow in Fortinet FortiOS 6.0.0 through 6.0.4, 5.6.0 through 5.6.10, 5.4.0 through 5.4.12, 5.2.14 and earlier and FortiProxy 2.0.0, 1.2.8 and earlier in the SSL VPN web portal may cause the SSL VPN web service termination for logged in users due to a failure to properly handle javascript href data when proxying webpages.
Affected Versions
| Product | Versions |
|---|---|
| Fortinet Fortinet FortiOS and FortiProxy | FortiOS 6.0.0 through 6.0.4, 5.6.0 through 5.6.10, 5.4.0 through 5.4.12, 5.2.14 and earlier, FortiProxy 2.0.0, 1.2.8 and earlier |
From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for Fortinet FortiOS and FortiProxy. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
- 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
Vendor Advisories
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
Not Sure If You Are Exposed?
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