Vulnerability in OpenSSL CMS and S/MIME Functions Exposes RSA Keys

CVE-2026-42768

What is CVE-2026-42768?

OpenSSL's CMS_decrypt and PKCS7_decrypt functions have a vulnerability that may allow attackers to exploit a Bleichenbacher-style attack. When an attacker gains access to CMS or S/MIME messages and can observe error codes or decryption output, they can potentially use the victim's application to decrypt or sign messages with their private RSA key. The risk arises in two scenarios: one without a recipient certificate causing the function to iterate through KeyTransRecipientInfo entries, and another where substitution of a key occurs when the recipient is not found. Proper mitigation involves using appropriate recipient certificates to prevent unauthorized attacks.

References