#VU50843 Improper Certificate Validation in Stunnel - CVE-2021-20230

Vulnerability identifier: #VU50843

Vulnerability risk: Medium

CVSSv4.0: 6.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-20230

CWE-ID: CWE-295

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Stunnel
Client/Desktop applications / Encryption software

Vendor: Stunnel.org

Description

The vulnerability allows a remote attacker to bypass implemented security restrictions.

The vulnerability exists due to improper client certificate validation, when redirect and verifyChain options are used. A remote attacker can bypass implemented security restrictions with a any valid certificated and gain access to sensitive information.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Stunnel: 5.00 - 5.56

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External links
https://www.redhat.com/security/data/cve/CVE-2021-20230.html
https://bugzilla.redhat.com/show_bug.cgi?id=1925226

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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.