ASA-SEC-016LowCisco ASACIS 2.5

ICMP to the device allowed from any address on an untrusted interface

Base severity

Low

Area

Administrators and Access

Platform

Cisco ASA

Evidence level

Derived0.90

Benchmark reference

CIS 2.5

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

Answering every ICMP message on the internet side helps discovery of the firewall and some reconnaissance.

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.

In ASDM: Configuration > Device Management > Management Access > ICMP, replace the any rule with rules for the monitoring addresses and add a last deny any rule for the interface. Apply and save.
On the CLI: no icmp permit any <nameif>, icmp permit <monitoring-network> <mask> echo <nameif>, icmp deny any <nameif>, and write memory.

Cisco ASA CLI

configure terminalno icmp permit any <nameif>icmp permit <monitoring-network> <mask> echo <nameif>icmp deny any <nameif>endwrite 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 icmp

Values to fill in3

<nameif>: The interface name (nameif)
<monitoring-network>: The monitoring network allowed to ping the device
<mask>: Its netmask

Before you type it2

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>).

How to confirm the fix

Run show running-config icmp and confirm the order.

Limits

Path MTU discovery needs unreachable messages; keep them if the design relies on it.

Compliance references

2.5

CIS Cisco ASA 9.x Firewall Benchmark v1.1.0

Covers part of the recommendation

Where a control aligns with a recommendation of the CIS Cisco ASA 9.x Firewall Benchmark v1.1.0, that recommendation is cited as a reference. Only that version was checked. A reference is not a certification.

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