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ConfigProof

All controls

ASA-SEC-025MediumCisco ASA

Site-to-site tunnel without Perfect Forward Secrecy

At a glance

Base severity

Medium

Area

IPSec VPN

Platform

Cisco ASA

Evidence level

Fact1.00

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

Without PFS every IPsec key derives from the same IKE key, so one compromised key exposes past and future traffic.

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.

  1. In ASDM: Configuration > Site-to-Site VPN > Advanced > Crypto Maps, edit the entry and check Enable Perfect Forwarding Secrecy with group 20 or 14. Apply and save.
  2. On the CLI: crypto map <map> <seq> set pfs group20, and write memory; the peer must match.

Command line

Cisco ASA CLI

configure terminalcrypto map <crypto-map> <sequence> set pfs group20endwrite memory

An example. Values in angle brackets are yours to supply; a finding on your own export fills in the names it read. Typed in configuration mode; write memory saves it, with no separate commit. Read every line first.

Read it back

show running-config crypto map
Values to fill in2
<crypto-map>
The crypto map
<sequence>
The crypto map entry's sequence number
Before you type it3
  • Written from the ASA 9.x command reference and not run on a device: read each line before you paste it.
  • In multiple context mode, type it in the context it applies to (changeto context <name>).
  • The far end has to offer the same proposal, so coordinate the change with whoever runs it.

How to confirm the fix

  • Run show crypto ipsec sa peer <peer> and confirm PFS is negotiated.

Limits

  • No limitation is recorded for this control beyond the one that applies to all of them: it reads a configuration export.

Compliance references

No benchmark recommendation is mapped to this control in this version.

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