Bug 1896739 (CVE-2020-25708) - CVE-2020-25708 libvncserver: libvncserver/rfbserver.c has a divide by zero which could result in DoS
Summary: CVE-2020-25708 libvncserver: libvncserver/rfbserver.c has a divide by zero wh...
Keywords:
Status: CLOSED ERRATA
Alias: CVE-2020-25708
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard:
Depends On: 1896740 1898077 1898078
Blocks: 1896743
TreeView+ depends on / blocked
 
Reported: 2020-11-11 12:39 UTC by Michael Kaplan
Modified: 2021-05-18 15:16 UTC (History)
5 users (show)

Fixed In Version: libvncserver 0.9.13
Doc Type: If docs needed, set a value
Doc Text:
A divide by zero flaw was found in libvncserver. This flaw allows a malicious client to send a specially crafted message that, when processed by the VNC server, leads to a floating-point exception, resulting in a denial of service. The highest threat from this vulnerability is to system availability.
Clone Of:
Environment:
Last Closed: 2021-05-18 14:36:07 UTC
Embargoed:

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Description Michael Kaplan 2020-11-11 12:39:52 UTC 
An issue was discovered in libvncserver-0.9.12. There is a divide by zero in rfbSendRectEncodingRaw function in libvncserver/rfbserver.c.
Attackers can launch a denial of service attack by sending a special message to the VNC server.

Upstream issue:
https://github.com/LibVNC/libvncserver/issues/409

Upstream commit:
https://github.com/LibVNC/libvncserver/commit/673c07a75ed844d74676f3ccdcfdc706a7052dba
Comment 1 Michael Kaplan 2020-11-11 12:39:58 UTC 
Acknowledgments:

Name: Kailong Zhu, Hui Huang, Lu Yu
Comment 2 Michael Kaplan 2020-11-11 12:40:02 UTC 
External References:

https://github.com/LibVNC/libvncserver/issues/409
https://github.com/LibVNC/libvncserver/commit/673c07a75ed844d74676f3ccdcfdc706a7052dba
Comment 3 Michael Kaplan 2020-11-11 12:40:40 UTC 
Created libvncserver tracking bugs for this issue:

Affects: epel-7 [bug 1896740]
Comment 7 DRC 2021-02-23 21:49:30 UTC 
NOTE: at least one commercial firewall has flagged TurboVNC connections as vulnerable to this CVE, but to the best of my knowledge and testing, LibVNCServer is the only TightVNC-compatible code base that is (was) vulnerable.  I was unable to reproduce the vulnerability with TightVNC 1.3.x, TigerVNC, or TurboVNC.  Refer to https://github.com/TurboVNC/turbovnc/pull/273#issuecomment-784498698.
Comment 9 Product Security DevOps Team 2021-05-18 14:36:07 UTC 
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2020-25708
Comment 10 errata-xmlrpc 2021-05-18 15:16:21 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:1811 https://access.redhat.com/errata/RHSA-2021:1811
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