CVE-2021-3601
Description
A flaw was found in the way OpenSSL will accept a certificate with explicitly set Basic Constraints to CA:FALSE as a valid CA if it is present in the trusted bundle. This flaw allows an attacker with access to a private key, of which the corresponding certificate is in the trust bundle, to use this flaw for MITM to any connection from the victim machine.
Statement
It was found that OpenSSL will accept a certificate with explicitly set Basic Constraints to CA:FALSE as a valid CA if it is present in the trusted bundle. The exploitability of this bug is limited; the attacker needs to get access to a private key of which the corresponding certificate is in the trust bundle. The attacker is able to leverage this certificate to MITM any connection from the victim machine, not just ones to the specific server that uses the self-signed certificate.
Mitigation
Red Hat recommends not to include self-signed server certificates in system trust bundle, even with CA:FALSE, as they are considered full-fledged Certificate Authorities.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 3.3 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | High | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | Low | N/A | N/A |
| Integrity Impact | Low | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:N
Acknowledgements
Red Hat would like to thank Hubert Kario for reporting this issue.
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