Title: XDMCP Infinite Loop Denial of Service Vulnerability
Severity: MODERATE
Description:
A programming flaw exists in OpenDis.c file of libX11 that could result in a denial of service against things listening to XDMCP, including xdm. By altering the contents of the server reply packet to a connection establishment request, it is possible to cause an infinite loop in the affected function. Doing this multiple times can cause a denial of service attack.
The flaw stems from the use of the dpy->resource_mask value, received from the network, to control a loop. By passing a mask value of 0, the loop will never end.
lib/X11/OpenDis.c, ~line 373
mask = dpy->resource_mask;
dpy->resource_shift = 0;
while (!(mask & 1)) {
dpy->resource_shift++;
mask = mask >> 1;
}
Affected Products:
- Debian Linux 2.2.0
- Open Group X 11.0.0R6
- Open Group X 11.0.0R6.1
- Open Group X 11.0.0R6.2
- Open Group X 11.0.0R6.3
- Open Group X 11.0.0R6.4
- RedHat Linux 6.2.0
- XFree86 X11R6 3.3.3
- XFree86 X11R6 3.3.4
- XFree86 X11R6 3.3.5
- XFree86 X11R6 3.3.6
- XFree86 X11R6 4.0.0
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