Bug 1860325 (CVE-2020-14405) - CVE-2020-14405 libvncserver: libvncclient/rfbproto.c does not limit TextChat size
Summary: CVE-2020-14405 libvncserver: libvncclient/rfbproto.c does not limit TextChat ...
Alias: CVE-2020-14405
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1860326 1860327 1860526 1860527
Blocks: 1860332
TreeView+ depends on / blocked
Reported: 2020-07-24 10:19 UTC by Marian Rehak
Modified: 2021-05-18 15:16 UTC (History)
4 users (show)

Fixed In Version: libvncserver 0.9.13
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Last Closed: 2021-05-18 14:34:56 UTC

Attachments (Terms of Use)

Description Marian Rehak 2020-07-24 10:19:00 UTC
An issue was discovered in LibVNCServer before 0.9.13. libvncclient/rfbproto.c does not limit TextChat size.

Upstream commit:


Comment 1 Marian Rehak 2020-07-24 10:19:34 UTC
Created libvncserver tracking bugs for this issue:

Affects: epel-7 [bug 1860326]
Affects: fedora-all [bug 1860327]

Comment 2 Todd Cullum 2020-07-24 22:07:54 UTC
Flaw Summary:

When receiving a remote framebuffer (RFB) textchat message, in HandleRFBServerMessage() of libvncclient/rfbproto.c, the routine does not validate the length of the message. The length of the message is immediately used in a call to malloc(). This could result in a memory allocation which is too large and could crash the vnc client, causing a temporary denial-of-service. The patch imposes a 10MB size limit on the textchat length and the routine will fail if it's above that length.

I've lowered the Impact to Moderate because triggering this flaw could lead to a temporary denial of service on the client. Exploitation would require a client user to connect to a malicious or compromised VNC server.

Comment 3 Todd Cullum 2020-07-24 22:22:09 UTC
vino is notaffected because it does not use the libvncclient functionality of libvncserver and thus the affected code is not shipped in the package; it only uses the server components.

Comment 6 Product Security DevOps Team 2021-05-18 14:34:56 UTC
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):


Comment 7 errata-xmlrpc 2021-05-18 15:16:12 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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