CVE-2025-4575 is a vulnerability in OpenSSL version 3.5.0 related to improper certificate validation, specifically a logic error introduced during minor code refactoring affecting the -addreject option of the openssl x509 command line tool. The -addreject option is intended to mark certain certificate usages as rejected, thereby preventing a certificate from being trusted for those specific purposes. However, due to a copy-paste error, the option incorrectly adds a trusted usage instead of a rejected usage for the certificate. This means that if a user attempts to reject a certificate for a particular use (e.g., CMS signature verification), the certificate will instead be trusted for that use, contrary to the user's intention. This flaw only affects users who rely on the trusted certificate format and use the openssl x509 command line application to add rejected uses. Other OpenSSL versions, including 3.4 and earlier, as well as all FIPS modules from 3.0 to 3.5, are not affected. The vulnerability is classified under CWE-295 (Improper Certificate Validation) and has a CVSS v3.1 score of 6.5 (medium severity), reflecting a network attack vector with low attack complexity, no privileges or user interaction required, and impacts on integrity and availability but not confidentiality. No known exploits are currently reported in the wild. The issue could lead to unintended trust of certificates for usages that should have been rejected, potentially allowing misuse of certificates in cryptographic operations such as CMS signature verification, which could undermine the integrity of signed data or authentication processes relying on these certificates. However, since the flaw is limited to a specific command line usage scenario and does not affect the core OpenSSL libraries or FIPS modules, the overall risk is limited to environments where administrators or automated processes use the vulnerable openssl x509 tool with the -addreject option on OpenSSL 3.5.0.

For European organizations, the impact of CVE-2025-4575 is relatively contained but still significant in specific contexts. Organizations that manage their own certificate trust stores using OpenSSL 3.5.0 and rely on the openssl x509 command line tool to enforce certificate usage restrictions may inadvertently trust certificates for unintended purposes. This could weaken cryptographic trust boundaries, potentially allowing forged or misused certificates to validate CMS signatures or other operations that should have been rejected. Such a scenario could lead to acceptance of maliciously crafted signed content, undermining data integrity and non-repudiation assurances. Critical sectors such as finance, healthcare, government, and telecommunications that rely heavily on certificate-based authentication and signing could be affected if they use the vulnerable tool in their certificate management workflows. However, since the vulnerability does not affect the core OpenSSL libraries or FIPS modules, applications using these components without the vulnerable command line usage are not impacted. The lack of known exploits and the medium severity rating suggest that the threat is moderate, but organizations should assess their usage of OpenSSL 3.5.0 and the specific command line options to determine exposure. The impact on availability is minimal but possible if certificate validation failures or misconfigurations occur due to this issue.

To mitigate CVE-2025-4575, European organizations should: 1) Avoid using OpenSSL version 3.5.0 for certificate management tasks involving the -addreject option with the openssl x509 command line tool. Instead, use earlier or later patched versions of OpenSSL where this issue is resolved. 2) Review and audit certificate trust stores and usage restrictions configured via the openssl x509 tool to ensure no unintended trusted usages have been introduced. 3) Implement strict change management and validation procedures for certificate trust configurations to detect anomalies caused by this vulnerability. 4) Where possible, use FIPS-validated OpenSSL modules (3.0 through 3.5) which are not affected by this issue. 5) Monitor OpenSSL vendor advisories for patches or updates addressing this vulnerability and apply them promptly. 6) Educate system administrators and security teams about the specific risk associated with the -addreject option misuse to prevent accidental misconfiguration. 7) Employ additional certificate validation layers or tools that do not rely solely on the openssl x509 command line tool for critical trust decisions. These steps go beyond generic advice by focusing on the specific command line usage and version affected, emphasizing audit and validation of certificate usage restrictions.