PSIRT Advisories

FortiOS is potentially vulnerable to a Heap buffer overflow.


A heap-based buffer overflow vulnerability in the processing of Link Control Protocol messages in FortiOS may allow a remote attacker with valid SSL VPN credentials to crash the SSL VPN daemon by sending a large LCP packet, when tunnel mode is enabled. Arbitrary code execution may be theoretically possible, albeit practically very difficult to achieve in this context.

Affected Products

FortiOS versions 5.6.12 and below. FortiOS versions 6.0.10 and below. FortiOS versions 6.2.4 and below. FortiOS versions 6.4.1 and below.


Please upgrade to FortiOS versions 5.6.13 or above. 
 Please upgrade to FortiOS versions 6.0.11 or above. 
 Please upgrade to FortiOS versions 6.2.5 or above. 
 Please upgrade to FortiOS versions 6.4.2 or above. 
 Workaround: Disable tunnel mode.


Fortinet is pleased to thank Communications Security Establishment (CSEC) for reporting this vulnerability under responsible disclosure.