IPsec proposal with a weak algorithm or DH group
At a glance
Base severity
Area
Platform
Evidence level
Benchmark reference
Reads the export, not the device
ConfigProof reads a configuration export. This control is evaluated against the objects in that file, and it reports what the file says. It does not connect to the device and sees no traffic, so a finding here describes the configuration, not what the firewall is doing right now.
Why it matters
DES, 3DES, MD5, SHA-1 and Diffie-Hellman groups 1, 2 and 5 no longer protect a tunnel against a capable attacker. A peer that accepts them may negotiate them.
How to fix it
Web interface
The steps below are written for the web interface. A finding raised on your own export carries the same steps with your object names filled in.
- Offer only AES (GCM preferred) with SHA-256 or better, and Diffie-Hellman groups 14, 19, 20 or 21, on both peers.
Command line
FortiOS CLI
config vpn ipsec phase1-interfaceedit <phase1-name>set proposal aes256gcm-prfsha384 aes256-sha256set dhgrp 20 19 14nextend
An example. Values in angle brackets are yours to supply; a finding on your own export fills in the names it read. FortiOS saves a change when you type next or end, with no separate commit. Read every line first.
Read it back
show vpn ipsec phase1-interface <phase1-name>Values to fill in1
- <phase1-name>
- The IPsec gateway to change
Before you type it3
- Written from the FortiOS CLI Reference, not yet run on a device. Read each line before typing it.
- On a device with VDOMs, type these inside the VDOM (config vdom, edit the VDOM) or inside config global for a global setting.
- The far end has to offer the same proposal, so coordinate the change with whoever runs it.
How to confirm the fix
- Change both ends in one window, and confirm the tunnel negotiates with the new proposal.
Limits
- IKE and IPsec proposals are read as the backup writes them; a proposal the backup leaves out is not judged.
Compliance references
No benchmark recommendation is mapped to this control in this version.
See it on your own firewall
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