IPsec uses weak algorithms (DES, 3DES, MD5)

What the audit found

One of your IPsec proposals or profiles (IP → IPsec) lists a weak algorithm: DES or 3DES for encryption, MD5 for integrity, or in the worst case null encryption. The finding names the proposal or profile concerned.

The audit reports this as medium severity. A weak algorithm in the list does not mean every tunnel uses it — the peers negotiate — but it means the router will accept it, and an attacker in the path may be able to steer a negotiation towards the weakest option both sides allow.

Why it matters

IPsec exists to keep tunnel traffic private and unaltered across untrusted networks. That guarantee is only as strong as the weakest algorithm you permit.

DES uses a 56-bit key and has been breakable by brute force since the late 1990s. 3DES is stronger but slow, limited to a 64-bit block size that makes it vulnerable to birthday attacks on long-lived sessions, and formally deprecated by NIST. MD5 has practical collision attacks and should not be used for anything security-related. null encryption is exactly what it sounds like: authenticated but readable.

The realistic risk depends on who is between your peers. A site-to-site tunnel across the internet passes through many networks you do not control. If it negotiates 3DES/MD5 because both sides still allow it, an adversary who records the traffic today may be able to read it later — and you will not know which proposal a tunnel settled on without checking.

The proposals also govern what the router accepts from remote users (L2TP/IPsec, IKEv2 road warriors). A client with weak defaults will happily connect with them, and the connection looks perfectly healthy in the log.

The good news: every device made in the last decade supports AES and SHA-2, and most current MikroTik models handle AES in hardware, so the modern set is usually faster than 3DES.

What it looks like in Winbox

Open IP → IPsec and look at the Proposals tab. Each proposal lists Auth. Algorithms and Encr. Algorithms; if md5, des, 3des or null appear, this is the finding. The Profiles tab holds the phase 1 (IKE) settings with the same kind of list under Hash Algorithms and Encryption Algorithm.

How to fix it

Update the proposal to modern algorithms and a strong DH group for perfect forward secrecy. Under IP → IPsec → Proposals, open the proposal the finding names and set its encryption algorithms to AES-256 (CBC and GCM), its authentication algorithm to SHA-256, and its PFS Group to a 2048-bit group (modp2048) or stronger, removing DES, 3DES, MD5 and null from the lists. If you have several proposals, change each one in turn rather than only the default.

Apply the equivalent change to the IKE profile under IP → IPsec → Profiles — AES-256 encryption, SHA-256 hash and a 2048-bit DH group — so that phase 1 is not the weak link.

Do this in coordination with the other end of each tunnel. IPsec only works when both peers share at least one common algorithm set; if you remove 3DES here and the remote site only offers 3DES, the tunnel will fail to establish. Change the remote side first (or add the new algorithms there before removing the old ones here), then update the router, then confirm each tunnel comes back up. Safe Mode does not help with a remote peer that cannot renegotiate, so schedule a maintenance window for site-to-site links.

Afterwards, open IP → IPsec → Installed SAs once the tunnels reconnect: each SA should show AES-256 and SHA-256, not 3DES or MD5, and Active Peers should list all expected peers as established. Confirm that no proposal or profile still lists a weak entry, then re-run the audit.

The full MKRouterKit report gives the exact commands for your configuration — with your interface names and subnets filled in, in the order that will not lock you out.

FAQ

The remote peer is an old device that only supports 3DES. What can I do?

Isolate the problem rather than accept it globally. Create a dedicated proposal and profile for that one peer, keep the weak algorithms only there, and use the modern set everywhere else. Then plan a replacement — a device that cannot do AES today has usually stopped receiving security updates as well.

Will AES-256 slow my tunnels down?

Almost never. Most current MikroTik models have hardware acceleration for AES, and AES-GCM in particular is very efficient. 3DES, by contrast, runs in software and is typically the slowest option available.

My tunnels currently negotiate AES anyway. Is the weak entry still a problem?

Yes, because you are relying on the other side to prefer the strong option. Removing the weak algorithms from the list guarantees the outcome instead of hoping for it, and it stops a misconfigured or malicious peer from talking the router down to 3DES.