CVE-2019-1543

ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for
every encryption operation. RFC 7539 specifies that the nonce value (IV)
should be 96 bits (12 bytes). OpenSSL allows a variable nonce length and
front pads the nonce with 0 bytes if it is less than 12 bytes. However it
also incorrectly allows a nonce to be set of up to 16 bytes. In this case
only the last 12 bytes are significant and any additional leading bytes are
ignored. It is a requirement of using this cipher that nonce values are
unique. Messages encrypted using a reused nonce value are susceptible to
serious confidentiality and integrity attacks. If an application changes
the default nonce length to be longer than 12 bytes and then makes a change
to the leading bytes of the nonce expecting the new value to be a new
unique nonce then such an application could inadvertently encrypt messages
with a reused nonce. Additionally the ignored bytes in a long nonce are not
covered by the integrity guarantee of this cipher. Any application that
relies on the integrity of these ignored leading bytes of a long nonce may
be further affected. Any OpenSSL internal use of this cipher, including in
SSL/TLS, is safe because no such use sets such a long nonce value. However
user applications that use this cipher directly and set a non-default nonce
length to be longer than 12 bytes may be vulnerable. OpenSSL versions 1.1.1
and 1.1.0 are affected by this issue. Due to the limited scope of affected
deployments this has been assessed as low severity and therefore we are not
creating new releases at this time. Fixed in OpenSSL 1.1.1c (Affected
1.1.1-1.1.1b). Fixed in OpenSSL 1.1.0k (Affected 1.1.0-1.1.0j).

Notes