CVE-2019-1551: rsaz_512_sqr overflow bug on x86_64

As per openssl upstream advisory:

There is an overflow bug in the x6464 Montgomery squaring procedure used in exponentiation with 512-bit moduli. No EC algorithms are affected. Analysis suggests that attacks against 2-prime RSA1024, 3-prime RSA1536, and DSA1024 as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH512 are considered just feasible. However, for an attack the target would have to re-use the DH512 private key, which is not recommended anyway. Also applications directly using the low level API BNmodexp may be affected if they use BNFLGCONSTTIME.

OpenSSL versions 1.1.1 and 1.0.2 are affected by this issue. However due to the low severity of this issue we are not creating new releases at this time. The 1.1.1 mitigation for this issue can be found in commit 419102400. The 1.0.2 mitigation for this issue can be found in commit f1c5eea8a.

— Red Hat

OpenSSL could allow a remote attacker to obtain sensitive information, caused by an overflow in the x6464 Montgomery squaring procedure used in exponentiation with 512-bit moduli. By performing a man-in-the-middle attack, a remote attacker could exploit this vulnerability to obtain sensitive information.

— IBM

There is an overflow bug in the x6464 Montgomery squaring procedure used in exponentiation with 512-bit moduli. No EC algorithms are affected. Analysis suggests that attacks against 2-prime RSA1024, 3-prime RSA1536, and DSA1024 as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH512 are considered just feasible. However, for an attack the target would have to re-use the DH512 private key, which is not recommended anyway. Also applications directly using the low level API BNmodexp may be affected if they use BNFLGCONSTTIME. Fixed in OpenSSL 1.1.1e (Affected 1.1.1-1.1.1d). Fixed in OpenSSL 1.0.2u (Affected 1.0.2-1.0.2t).