#VU28557 Man-in-the-Middle (MitM) attack in GnuTLS - CVE-2020-13777

Vulnerability identifier: #VU28557

Vulnerability risk: Medium

CVSSv4.0: 2.1 [CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/U:Green]

CVE-ID: CVE-2020-13777

CWE-ID: CWE-300

Exploitation vector: Local network

Exploit availability: Yes

Vulnerable software:
GnuTLS
Universal components / Libraries / Libraries used by multiple products

Vendor: GnuTLS

Description

The vulnerability allows a remote attacker to perform Man-in-the-Middle (MitM) attack.

The vulnerability exists due to regression, introduced into the TLS protocol implementation that caused the TLS server to not securely construct a session ticket encryption key considering the application supplied secret. A remote attacker can bypass authentication in TLS 1.3 and recover previous conversations in TLS 1.2

Mitigation
Install updates from vendor's website.

Vulnerable software versions

GnuTLS: 3.6.4 - 3.6.13

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External links
https://www.gnutls.org/security-new.html#GNUTLS-SA-2020-06-03
https://gitlab.com/gnutls/gnutls/-/issues/1011

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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 local network (LAN).

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.