The F5 BIG-IP appliance that provides intermediary services for SMTP must inspect inbound and outbound SMTP and Extended SMTP communications traffic for protocol compliance and protocol anomalies.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-266147	F5BI-AP-300041	SV-266147r1024374_rule		Medium

Description

Application protocol anomaly detection examines application layer protocols such as SMTP to identify attacks based on observed deviations in the normal RFC behavior of a protocol or service. This type of monitoring allows for the detection of known and unknown exploits which exploit weaknesses of commonly used protocols. Since protocol anomaly analysis examines the application payload for patterns or anomalies, an SMTP proxy must be included in the ALG. This ALG will be configured to inspect inbound and outbound SMTP and extended SMTP communications traffic to detect protocol anomalies such as malformed message and command insertion attacks.

STIG	Date
F5 BIG-IP TMOS ALG Security Technical Implementation Guide	2025-06-09

Details

Check Text (C-70071r1023687_chk)

If the BIG-IP appliance does not provide intermediary/proxy services for SMTP communications traffic, this is not applicable.

SMTP Profile:
From the BIG-IP GUI:
1. Local Traffic.
2. Profiles.
3. Services.
4. SMTP.
5. Click the name of the SMTP profile.
6. Verify "Protocol Security" is checked.

SMTP Virtual Server:
1. Local Traffic.
2. Virtual Servers.
3. Virtual Server List.
4. Click the name of the SMTP virtual server.
5. Verify the SMTP profile is selected in the "SMTP Profile" drop-down list.

If the BIG-IP appliance is not configured to inspect inbound and outbound SMTP and Extended SMTP communications traffic for protocol compliance and protocol anomalies, this is a finding.

Fix Text (F-69974r1023688_fix)

SMTP Profile:
From the BIG-IP GUI:
1. Local Traffic.
2. Profiles.
3. Services.
4. SMTP.
5. Click the name of the SMTP profile.
6. Check "Protocol Security".
7. Click "Update".

SMTP Virtual Server:
1. Local Traffic.
2. Virtual Servers.
3. Virtual Server List.
4. Click the name of the SMTP virtual server.
5. Select the SMTP profile from the "SMTP Profile" drop-down list.
6. Click "Update".

Refer to vendor documentation for more information.