SNA Server/SnaBase Traps Receive Invalid Client Logon Message (161777)

SYMPTOMS

The SNA Server or SnaBase process will encounter an access violation (AV) when receiving a badly formatted client logon challenge message. This leads to the following problems:

Users with active sessions may find that their computers stop responding and eventually they lose their host sessions. New users will be unable to connect through SNA Server until the computer running SNA Server is restarted.
The following Windows NT application event log message occurs:
Event ID: 624
Source: SNA Server
Creating dump file C:\SNA\traces\snadump.log for SNASERVR.DBG

A Drwtsn32.log entry is created that indicates an application exception error occurred in Snaservr.dbg:

      Application exception occurred:
           App: snaservr.DBG (pid=<process ID>)  (or snabase.DBG)
           Exception number: c0000005 (access violation)

      State Dump for Thread Id <thread ID>

      eax=0000002a ebx=00000000 ecx=00000000 edx=00000000 esi=01213463
      edi=0000002a
      eip=00ab956b esp=4cd4fa14 ebp=62f5002a iopl=0         nv up ei pl nz
      na pe nc
      cs=001b  ss=0023  ds=0023  es=0023  fs=0038  gs=0000
      efl=00000202

      function: GetSecField
      [...]
      FAULT ->00ab956b 0fbf4206   movsx eax,word ptr [edx+0x6]
      ds:005de923=????

The SNA Server service must be restarted to recover. If an SnaBase failure occurs, both the SnaBase and SNA Server services must be restarted to recover.

CAUSE

The cause of the improperly formatted client logon challenge message is unknown. The person who experienced this problem was using SNA Server 2.1 Windows 3.x client computers with a third-party (Korean) TCP/IP protocol stack. SNA Server did not expect such an invalid message to be received from a client computer, causing the server to attempt to process the message without validating the format. This led to an SNA Server access violation.

STATUS

Microsoft has confirmed this to be a problem in SNA Server version 2.11. This problem has been corrected in the latest U.S. service pack for SNA Server version 2.11. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K