FortiMail's SaltHash vulnerable to extension attacks

Summary

A missing cryptographic step in the implementation of the hash digest algorithm in FortiMail may allow an unauthenticated attacker to tamper with signed URLs by appending further data which allows bypass of signature verification.

Affected Products

FortiMail 6.4.4 and below,
FortiMail 6.2.6 and below.

Solutions

Upgrade to FortiMail version 7.0.0.
Upgrade to FortiMail version 6.4.5.

Acknowledgement

Internally discovered and reported by Giuseppe Cocomazzi of the Fortinet PSIRT Team.

Timeline

2021-07-07: Initial publication