CVE-2021-3450
Description
A flaw was found in openssl. The flag that enables additional security checks of certificates present in a certificate chain was not enabled allowing a confirmation step to verify that certificates in the chain are valid CA certificates is bypassed. The highest threat from this vulnerability is to data confidentiality and integrity.
Statement
This flaw affects openssl 1.1.1h and above only, older versions are not affected by this flaw.
Mitigation
The following conditions have to be met for an application compiled with OpenSSL to be vulnerable:
- the CA trusted by the system must issue or have issued certificates that don't include basic Key Usage extension.
- the CA certificates must not have path length constraint set to a value that would limit the certificate chain to just the subscriber certificates (i.e. CA certificate just above the subscriber cert must not have 0 as the path length constraint, and any CA above it must not have it increase by more than 1 for every level in the hierarchy)
- the attacker needs to have access to such subscriber certificate (without basic Key Usage and linking up to CAs without path length constraints or not effectively constraining certs issued by this certificate)
- the application under attack must use the X509_V_FLAG_X509_STRICT flag and must not set purpose for the certificate verification
if any of the above conditions are not met then the application compiled with OpenSSL is not vulnerable to the CVE.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.4 | 7.4 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Understanding the Weakness (CWE)
Integrity,Authentication
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity
When a certificate is invalid or malicious, it might allow an attacker to spoof a trusted entity by interfering in the communication path between the host and client. The product might connect to a malicious host while believing it is a trusted host, or the product might be deceived into accepting spoofed data that appears to originate from a trusted host.
Acknowledgements
Red Hat would like to thank the OpenSSL Project for reporting this issue. Upstream acknowledges Benjamin Kaduk and Xiang Ding and others (Akamai) as the original reporters.
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