CVE-2021-20230

HIGH
7.5
CVSS Score
Published: February 23, 2021 at 04:34 PM UTC
Updated: June 17, 2026 at 03:33 AM UTC
1 product affected across 1 vendorStunnel

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Severity
HIGH7.5
Exploit prediction
EPSS 1%

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 5.575.57
Affected range stops below 5.57, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

References (3)

x_refsource_MISCIssue TrackingThird Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1925226
Vendor Advisoryx_refsource_GENTOOThird Party Advisory
https://security.gentoo.org/glsa/202105-02

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-295

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