#VU47533 Improper Certificate Validation in TigerVNC - CVE-2020-26117

Vulnerability identifier: #VU47533

Vulnerability risk: Medium

CVSSv4.0: 1.2 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2020-26117

CWE-ID: CWE-295

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
TigerVNC
Web applications / Modules and components for CMS

Vendor: tigervnc.org

Description

The vulnerability allows a remote attacker to perform a MitM attack.

The vulnerability exists due to improper TLS certificate validation in rfb/CSecurityTLS.cxx and rfb/CSecurityTLS.java in TigerVNC. Any previously accepted certificate will be considered trusted, meaning that the owner of a certificate could impersonate any server after a client had added an exception.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

TigerVNC: 1.0 - 1.10.90

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External links
https://bugzilla.opensuse.org/show_bug.cgi?id=1176733
https://github.com/TigerVNC/tigervnc/commit/20dea801e747318525a5859fe4f37c52b05310cb
https://github.com/TigerVNC/tigervnc/commit/7399eab79a4365434d26494fa1628ce1eb91562b
https://github.com/TigerVNC/tigervnc/commit/b30f10c681ec87720cff85d490f67098568a9cba
https://github.com/TigerVNC/tigervnc/commit/f029745f63ac7d22fb91639b2cb5b3ab56134d6e
https://github.com/TigerVNC/tigervnc/releases/tag/v1.11.0
https://lists.debian.org/debian-lts-announce/2020/10/msg00007.html

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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.