CVE-2023-27997 Fortinet FortiOS and FortiProxy SSL-VPN Heap-Based Buffer Overflow Vulnerability
Fortinet FortiOS and FortiProxy SSL-VPN contain a heap-based buffer overflow vulnerability which can allow an unauthenticated, remote attacker to execute code or commands via specifically crafted requests.
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 13 Jun 2023.
- CISA lists it as known to be used in ransomware campaigns.
- Rated Critical severity (CVSS 9.2, 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 1,242 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
A heap-based buffer overflow vulnerability [CWE-122] in FortiOS version 7.2.4 and below, version 7.0.11 and below, version 6.4.12 and below, version 6.0.16 and below and FortiProxy version 7.2.3 and below, version 7.0.9 and below, version 2.0.12 and below, version 1.2 all versions, version 1.1 all versions SSL-VPN may allow a remote attacker to execute arbitrary code or commands via specifically crafted requests.
Affected Versions
| Product | Versions |
|---|---|
| Fortinet FortiOS-6K7K | 7.0.10 7.0.5 6.4.12 6.4.10 6.4.8 6.4.6 |
| Fortinet FortiProxy | 7.2.0 to 7.2.3 7.0.0 to 7.0.9 2.0.0 to 2.0.12 1.2.0 to 1.2.13 1.1.0 to 1.1.6 |
| Fortinet FortiOS | 7.2.0 to 7.2.4 7.0.0 to 7.0.11 6.4.0 to 6.4.12 6.2.0 to 6.2.13 6.0.0 to 6.0.16 |
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 SSL-VPN. 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
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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