#VU3076 Heap-based buffer overflow in LibVNCServer - CVE-2016-9941

Vulnerability identifier: #VU3076

Vulnerability risk: Medium

CVSSv4.0: 4.8 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2016-9941

CWE-ID: CWE-119

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
LibVNCServer
Server applications / Remote management servers, RDP, SSH

Vendor: LibVNC

Description
The vulnerability allows a remote attacker to execute arbitrary code on vulnerable client system.

A heap-based buffer overflow vulnerability exists due to boundary error in rfbproto.c in LibVNCClient software, which is bundled with LibVNCServer. A remote attacker can trick the victim to connect to malicious VNC server, send a specially crafted FramebufferUpdate message containing a subrectangle outside of the client drawing area and trigger buffer overflow.

Successful exploitation of the vulnerability may allow an attacker to execute arbitrary code on vulnerable VNC client.

Mitigation
Update to version 0.9.11:
https://github.com/LibVNC/libvncserver/tree/LibVNCServer-0.9.11

Vulnerable software versions

LibVNCServer: 0.9.9 - 0.9.10

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External links
https://github.com/LibVNC/libvncserver/pull/137
https://github.com/LibVNC/libvncserver/releases/tag/LibVNCServer-0.9.11

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.