TFTPD32 Long FileName Remote Denial of Service

By Sowhat
12.JAN.2005
http://secway.org/advisory/ad20050112.txt

Product Affected:
tftpd 2.74 and prior

Impact:
Low

OSVDB ID: 12898

(1) Introduction

Tftpd32 is a bundle including a full featured TFTP server, a TFTP client,
a DHCP server and a Syslog server.
Tftpd32 is designed for Windows 95/NT/2000/XP.
"Tftpd32 recommended by Cisco, HP  and other companies" --From the author's webpage.

For more information:
http://perso.wanadoo.fr/philippe.jounin/tftpd32.html

(2) Details
A vulnerability in tftpd32 may allow remote attackers crash the tftpd32 and 
therefore cause a Denial of Service.

aviram(@)beyondsecurity.com had reported "TFTPD32 Buffer Overflow Vulnerability 
(Long filename)" to bugtraq. And it seems that the author fixed the problem in v2.51.
But during the audit, I found that tftpd32 is still vulnerable to "Long Filenmae" issues.

C:\Windows\System32>tftp -i 192.168.0.1 get AAAAA...[about 508 'A' here]...AA

The tftpd32 will print the following error messages 2 times:
"Error:RecvFrom Returns 10040 <"A message sent on a datagram socket was larger than 
the internal message buffer or some other network limit, or the buffer used to 
receive a datagram into was smaller than the datagram itself.">"
Then, it will dead. 

But this vulnerability seems very unstable and it's non-exploitable.
the tftpd32 will not dead immediately, usually 10-15 seconds after the request,
and some times you need to "get" 2-3 times.

(3) Solution

Waitting for the author's update

(4) Author Response

I have sent an email to the author BUT no reply yet.

Update: 14.Jan.2005 The author replied that the problem will be fixed in next release.