This indicates an attack attempt against a stack-based buffer-overflow vulnerability in Novell GroupWise (GW) WebAccess.
The vulnerability is caused by an error when the vulnerable software handles long base64 data. It allows a remote attacker to execute arbitrary code via long base64 data in an HTTP Basic Authentication request.
Novell GroupWise (GW) WebAccess 7.0 SP2 and prior.
Apply the patch, available from the vendor's web site: