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||FWTK x-gw format bug
||26th October 2000
geekgang Security Advisory [gsa2000-01]
© Copyright 2000 geekgang
ID: geekgang GSA2000-01 01 v1.0
Topic: FWTK x-gw format bug
Status: Release 26th October, 2000
Credit: Pekka Savola found the potential problem in the code
The x-gw (X Windows gateway) component of the TIS Firewall Toolkit
(FWTK) contains a format bug vulnerability that may be exploitable
within some installations, allowing users to execute arbitrary code.
The FWTK contains a set of proxy applications that are designed to aid a
computing professional in building a firewall system. It is not a
complete firewall product within itself. As such it is impossible to
ascertain all the different configurations in which the various parts of
the FWTK have been installed.
The x-gw component is designed to proxy connections bewteen X Windows
clients and servers. It would normally be invoked via the tn-gw (Telnet
gateway) component of the FWTK. Installations using this tn-gw
invocation method of the x-gw are not vulnerable to this problem due to
pre-processing of input data that is performed by the tn-gw.
Installations using any other method to invoke the x-gw should check
their vulnerability status.
The x-gw takes the X Windows display to connect to as a command line
parameter or environment variable. It performs some sanity checking on
this input and reports an error if the checks fail. The function that
outputs the error message has a format bug, and uses the supplied
display string as part of the output.
The function at fault is pmsg() in the source file x-gw/pmsg.c
--- x-gw/pmsg.c.orig Mon Oct 23 13:21:26 2000
+++ x-gw/pmsg.c Mon Oct 23 13:22:36 2000
@@ -37,9 +37,9 @@
buf[sizeof(buf)-1] = '\0';
- if( uselog ) syslog( LLEV, buf );
+ if( uselog ) syslog( LLEV, "%s", buf );
- fprintf( stderr, buf );
+ fprintf( stderr, "%s", buf );
An exploit for this vulnerability will be made available on the geekgang
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