## Security Advisory #2020-06 (last updated on 2020-04-15)  
Title: Stack-based buffer overflow in CDE libDtSvc  
Application: Common Desktop Environment 2.3.1 and earlier  
Common Desktop Environment 1.6 and earlier2020-06-cde-libDtSvc.txt  
Platforms: Oracle Solaris 10 1/13 (Update 11) and earlier  
Other platforms are potentially affected (see below)  
Description: A difficult to exploit stack-based buffer overflow in the  
libDtSvc library distributed with CDE may allow local users to  
corrupt memory and potentially execute aritrary code in order  
to escalate privileges  
Author: Marco Ivaldi <>  
Vendor Status: Oracle <> notified on 2019-12-15  
CERT/CC notified on 2019-12-15 (tracking VU#308289)  
CVE Name: CVE-2020-2851  
CVSS Vector: CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H (Base Score: 7.8)  
1. Abstract.  
A difficult to exploit stack-based buffer overflow in the _DtCreateDtDirs()  
function in the Common Desktop Environment version distributed with Oracle  
Solaris 10 1/13 (Update 11) and earlier may allow local users to corrupt memory  
and potentially execute arbitrary code in order to escalate privileges via a  
long X11 display name. The vulnerable function is located in the libDtSvc  
library and can be reached by executing the setuid program dtsession.  
Note that Oracle Solaris CDE is based on the original CDE 1.x train, which is  
different from the CDE 2.x codebase that was later open sourced. In detail, the  
open source CDE is not affected by this specific vulnerability, but following  
our report some additional work has been done by its maintainers to properly  
check bounds in the libDtSvc library. Most notably, insecure calls to strncat()  
that caused buffer overflows have been fixed.  
2. Example Attack Session.  
In order to reproduce this bug, the following commands can be used:  
bash-3.2$ cat /etc/release  
Oracle Solaris 10 1/13 s10x_u11wos_24a X86  
Copyright (c) 1983, 2013, Oracle and/or its affiliates. All rights reserved.  
Assembled 17 January 2013  
bash-3.2$ uname -a  
SunOS nostalgia 5.10 Generic_147148-26 i86pc i386 i86pc  
bash-3.2$ id  
uid=54322(raptor) gid=1(other)  
bash-3.2$ grep /etc/hosts aaaa:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa  
[activate a valid display on]  
/usr/dt/bin/dtsession -display aaaa:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa:0  
Segmentation Fault  
3. Discussion.  
The overflow occurs in the following code snippet of Oracle Solaris CDE (the  
Ghidra decompiler is probably doing something wrong as some variables seem to  
overlap, however its output is good enough for the purpose of this discussion):  
char * _DtCreateDtDirs(int param_1)  
char local_f0 [104];  
char local_88 [112];  
char *heap_path2;  
char *tmp_ptr1;  
char *home;  
undefined *local_c;  
undefined local_8 [4];  
if (param_1 != 0) {  
strcpy(local_f0,*(char **)(param_1 + 0x80));  
strcpy(local_88,*(char **)(param_1 + 0x80));  
An X11 display data structure is passed to the _DtCreateDtDirs() function as  
its only parameter (param_1 in the pseudocode above). It contains the X11  
display name at offset 0x80. This display name is copied into the stack buffers  
local_f0 and local_88 using the insecure function strcpy() twice, therefore two  
overflows occur.  
Based on the inferred stack layout, the following local variables are  
overflowed into before the saved return address can be reached:  
This complicates exploitation, in particular because the heap_path2 and  
tmp_ptr1 pointers get in the way. A skilled attacker might be able to overwrite  
all variables with safe data and leverage memory corruption to obtain arbitrary  
code execution. However, there is an additional challenge: the ability to  
control a hostname to be passed in the X11 display name string. In our PoC  
above we have edited /etc/hosts, but this is obviously not possible for an  
unprivileged local attacker. A DNS server under the control of the attacker may  
be used for this purpose, but such an approach would introduce a number of  
additional complications.  
That said, as a rule of thumb all memory corruption issues have the potential  
to become serious security vulnerabilities until otherwise proven. Therefore,  
we recommend to treat this bug as a potential security vulnerability and to fix  
it as such.  
4. Affected Platforms.  
All platforms shipping the Common Desktop Environment are potentially affected.  
This includes:  
* Oracle Solaris 10 1/13 (Update 11) and earlier [default installation]  
According to the CDE Wiki, the following platforms are officially supported:  
* All Official Ubuntu variants 12.04 - 18.04  
* Debian 6, 7, 8, 9  
* Fedora 17 at least  
* Archlinux  
* Red Hat  
* Slackware 14.0  
* OpenBSD  
* NetBSD  
* FreeBSD 9.2, 10.x, 11.x  
* openSUSE Tumbleweed (gcc7)  
* openSUSE Leap 4.2 (gcc4)  
* SUSE 12 SP3 (gcc4)  
* Solaris, OpenIndiana  
5. Fix.  
The maintainers of the open source CDE 2.x version have issued the following  
Oracle, which maintains a different CDE codebase based on the 1.x train, has  
assigned the tracking# S1240932 and has released a fix for all affected and  
supported versions of Solaris in the Critical Patch Update (CPU) of April 2020.  
As a workaround, it is also possible to remove the setuid bit from the  
vulnerable executable as follows (note that this might prevent it from working  
bash-3.2# chmod -s /usr/dt/bin/dtsession  
Please note that during the audit many other potentially exploitable bugs have  
surfaced in libDtSvc and in the Common Desktop Environment in general.  
Therefore, removing the setuid bit from all CDE binaries is recommended,  
regardless of patches released by vendors.  
Copyright (c) 2020 Marco Ivaldi and All rights reserved.