Bug ID 963237: Non-EDNS response with RCODE FORMERR are blocked by AFM MARFORM vector.

Last Modified: Sep 13, 2023

Affected Product(s):
BIG-IP AFM(all modules)

Known Affected Versions:
13.1.0, 13.1.0.1, 13.1.0.2, 13.1.0.3, 13.1.0.4, 13.1.0.5, 13.1.0.6, 13.1.0.7, 13.1.0.8, 13.1.1, 13.1.1.2, 13.1.1.3, 13.1.1.4, 13.1.1.5, 13.1.3, 13.1.3.1, 13.1.3.2, 13.1.3.3, 13.1.3.4, 13.1.3.5, 13.1.3.6, 13.1.4, 13.1.4.1, 13.1.5, 13.1.5.1, 14.0.0, 14.0.0.1, 14.0.0.2, 14.0.0.3, 14.0.0.4, 14.0.0.5, 14.0.1, 14.0.1.1, 14.1.0, 14.1.0.1, 14.1.0.2, 14.1.0.3, 14.1.0.5, 14.1.0.6, 14.1.2, 14.1.2.1, 14.1.2.2, 14.1.2.3, 14.1.2.4, 14.1.2.5, 14.1.2.6, 14.1.2.7, 14.1.2.8, 14.1.3, 14.1.3.1, 15.0.0, 15.0.1, 15.0.1.1, 15.0.1.2, 15.0.1.3, 15.0.1.4, 15.1.0, 15.1.0.1, 15.1.0.2, 15.1.0.3, 15.1.0.4, 15.1.0.5, 15.1.1, 15.1.2, 15.1.2.1, 16.0.0, 16.0.0.1, 16.0.1

Fixed In:
16.1.0, 16.0.1.1, 15.1.3, 14.1.4

Opened: Nov 06, 2020

Severity: 3-Major

Symptoms

When a client sends a DNS request to a NON EDNS capable server, the server may send a legitimate response with RCODE FORMERR and no DNS data. The MALFORM DNS vector blocks those requests.

Impact

AFM erroneously detects an attack and mitigates it, and the client does not get a responses from the EDNS server

Conditions

-- The client sends a DNS request to NON EDNS capable server -- The server replies with RCODE FORMERR and no DNS data.

Workaround

Disable DNS MALFORM vector mitigation or put the EDNS server in allow list.

Fix Information

None

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips