An issue was discovered in the supplementary Go cryptography library, golang.org/x/crypto, before v0.0.0-20190320223903-b7391e95e576. A flaw was found in the amd64 implementation of the golang.org/x/crypto/salsa20 and golang.org/x/crypto/salsa20/salsa packages. If more than 256 GiB of keystream is generated, or if the counter otherwise grows greater than 32 bits, the amd64 implementation will first generate incorrect output, and then cycle back to previously generated keystream. Repeated keystream bytes can lead to loss of confidentiality in encryption applications, or to predictability in CSPRNG applications.

The Go SSH library (x/crypto/ssh) by default does not verify host keys, facilitating man-in-the-middle attacks. Default behavior changed in commit e4e2799 to require explicitly registering a hostkey verification mechanism.