CVE-2017-3736: Infoleak

OpenSSL could allow a remote attacker to obtain sensitive information, caused by a carry propagation flaw in the x8664 Montgomery squaring function bnsqrx8xinternal(). An attacker with online access to an unpatched system could exploit this vulnerability to obtain information about the private key.

— IBM

There is a carry propagating bug in the x8664 Montgomery squaring procedure in OpenSSL before 1.0.2m and 1.1.0 before 1.1.0g. No EC algorithms are affected. Analysis suggests that attacks against RSA and DSA as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH are considered just feasible (although very difficult) because most of the work necessary to deduce information about a private key may be performed offline. The amount of resources required for such an attack would be very significant and likely only accessible to a limited number of attackers. An attacker would additionally need online access to an unpatched system using the target private key in a scenario with persistent DH parameters and a private key that is shared between multiple clients. This only affects processors that support the BMI1, BMI2 and ADX extensions like Intel Broadwell (5th generation) and later or AMD Ryzen.

There is a carry propagating bug in the x8664 Montgomery squaring procedure. No EC algorithms are affected. Analysis suggests that attacks against RSA and DSA as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH are considered just feasible (although very difficult) because most of the work necessary to deduce information about a private key may be performed offline. The amount of resources required for such an attack would be very significant and likely only accessible to a limited number of attackers. An attacker would additionally need online access to an unpatched system using the target private key in a scenario with persistent DH parameters and a private key that is shared between multiple clients.

This only affects processors that support the BMI1, BMI2 and ADX extensions like Intel Broadwell (5th generation) and later or AMD Ryzen.

Note: This issue is very similar to CVE-2017-3732 and CVE-2015-3193 but must be treated as a separate problem.

External References:

https://www.openssl.org/news/secadv/20171102.txt

— Red Hat