Bug ID 1849585: A correctly encoded long Authorization param triggers 'illegal base64 value' vaiolation

Last Modified: Oct 15, 2025

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

Known Affected Versions:
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, 15.1.3, 15.1.3.1, 15.1.4, 15.1.4.1, 15.1.5, 15.1.5.1, 15.1.6, 15.1.6.1, 15.1.7, 15.1.8, 15.1.8.1, 15.1.8.2, 15.1.9, 15.1.9.1, 15.1.10, 15.1.10.2, 15.1.10.3, 15.1.10.4, 15.1.10.5, 15.1.10.6, 16.1.0, 16.1.1, 16.1.2, 16.1.2.1, 16.1.2.2, 16.1.3, 16.1.3.1, 16.1.3.2, 16.1.3.3, 16.1.3.4, 16.1.3.5, 16.1.4, 16.1.4.1, 16.1.4.2, 16.1.4.3, 16.1.5, 16.1.5.1, 16.1.5.2, 16.1.6, 17.0.0, 17.0.0.1, 17.0.0.2, 17.1.0, 17.1.0.1, 17.1.0.2, 17.1.0.3, 17.1.1, 17.1.1.1, 17.1.1.2, 17.1.1.3, 17.1.1.4, 17.1.2, 17.1.2.1, 17.1.2.2, 17.5.0, 17.5.1, 17.5.1.2

Fixed In:
17.5.1.3, 17.1.3

Opened: Mar 10, 2025

Severity: 3-Major

Symptoms

A correctly encoded base64 string that is over 8192 triggers 'illegal base64 value' violation

Impact

False positive with 'illegal base64 value'

Conditions

Authorization param is longer than 8192 chars

Workaround

Disable the violation

Fix Information

Introduced a new BD internal max_header_length. Default is 8192 that is the same value as it was. If you want to let ASM handling auth-param longer than 8192, set larger value than the auth-param with this internal.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips