This indicates an attempt to exploit a cross-site scripting (XSS) vulnerability in Session Initiation Protocol (SIP), a VoIP signaling protocol.
The vulnerability is caused by the protocol not properly filtering some header field that's coming from the SIP message. An attacker may exploit this to perform XSS injection.
Linksys SPA Linksys SPA-941 (Version 5.1.8)
System compromise: Cross-site scripting.
Currently we are not aware of any officially released patch or update.