Vulnerability identifier: #VU55489

Vulnerability risk: Medium

CVSSv3.1: 5.7 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N/E:U/RL:O/RC:C]

CVE-ID: CVE-2021-32066

CWE-ID: CWE-295

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Ruby
Universal components / Libraries / Scripting languages

Vendor: Ruby

Description

The vulnerability allows a remote attacker to perform MitM attack.

The vulnerability exists in Net::IMAP in Ruby, due to the gem does not raise an exception when StartTLS fails with an an unknown response. A remote attacker can perform a man-in-the-middle (MitM) attack.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Ruby: 2.6.0 - 3.0.1

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External links
http://github.com/ruby/ruby/commit/a21a3b7d23704a01d34bd79d09dc37897e00922a
http://www.ruby-lang.org/en/news/2021/07/07/starttls-stripping-in-net-imap/
http://hackerone.com/reports/1178562

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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.