UBUNTU-CVE-2021-20230

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    UBUNTU-CVE-2021-20230

    Published: 23 Feb 2021Last Modified: 4 Feb 2026
    Upstream:
    CVE-2021-20230
    Aliases:
    USN-6901-1

    Summary:

    Details: A flaw was found in stunnel before 5.57, where it improperly validates client certificates when it is configured to use both redirect and verifyChain options. This flaw allows an attacker with a certificate signed by a Certificate Authority, which is not the one accepted by the stunnel server, to access the tunneled service instead of being redirected to the address specified in the redirect option. The highest threat from this vulnerability is to confidentiality.

    References: https://ubuntu.com/security/CVE-2021-20230, https://github.com/mtrojnar/stunnel/commit/ebad9ddc4efb2635f37174c9d800d06206f1edf9, https://bugzilla.redhat.com/show_bug.cgi?id=1925226, https://bugzilla.suse.com/show_bug.cgi?id=1177580, https://www.cve.org/CVERecord?id=CVE-2021-20230, https://ubuntu.com/security/notices/USN-6901-1

    Affected packages

    Package

    Name: stunnel4

    Purl: pkg:deb/ubuntu/stunnel4@3:5.44-1ubuntu3+esm1?arch=source&distro=esm-apps/bionic

    Affected ranges

    Type: ECOSYSTEM

    Events:

    Introduced- 0
    Fixed -3:5.44-1ubuntu3+esm1

    Affected versions

    3:5.39-2

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High
    UBUNTU-CVE-2021-20230 | CVE-DB