How to fix Alternative chains certificate forgery (CVE-2015-1793):Critical OpenSSL vulnerability could allow attackers to intercept secure communications.
What is it:
An error in the implementation of the alternative certificate chain logic could allow an attacker to cause certain checks on untrusted certificates to be bypassed, such as the CA flag, enabling them to use a valid leaf certificate to act as a CA and "issue" an invalid certificate. Reported by Adam Langley and David Benjamin (Google/BoringSSL).Fixed in OpenSSL 1.0.2d (Affected 1.0.2c, 1.0.2b)Fixed in OpenSSL 1.0.1p (Affected 1.0.1o, 1.0.1n) ===================================================================== How to Fix it: Alternative chains certificate forgery (CVE-2015-1793) ==================================================================== Severity: High During certificate verification, OpenSSL (starting from version 1.0.1n and 1.0.2b) will attempt to find an alternative certificate chain if the first attempt to build such a chain fails. An error in the implementation of this logic can mean that an attacker could cause certain checks on untrusted certificates to be bypassed, such as the CA flag, enabling them to use a valid leaf certificate to act as a CA and "issue" an invalid certificate. This issue will impact any application that verifies certificates including SSL/TLS/DTLS clients and SSL/TLS/DTLS servers using client authentication. This issue affects OpenSSL versions 1.0.2c, 1.0.2b, 1.0.1n and 1.0.1o. OpenSSL 1.0.2b/1.0.2c users should upgrade to 1.0.2d OpenSSL 1.0.1n/1.0.1o users should upgrade to 1.0.1p This issue was reported to OpenSSL on 24th June 2015 by Adam Langley/David Benjamin (Google/BoringSSL). The fix was developed by the BoringSSL project. More Information on this vulnerability: https://www.acmetek.com/Support/the-new-alternative-chains-certificate-forgery-vulnerability-cve-2015-1793/