libcurl versions from 7.34.0 to before 7.64.0 are vulnerable to a heap out-of-bounds read in the code handling the end-of-response for SMTP. If the buffer passed to `smtp_endofresp()` isn't NUL terminated and contains no character ending the parsed number, and `len` is set to 5, then the `strtol()` call reads beyond the allocated buffer. The read contents will not be returned to the caller.
https://www.oracle.com/technetwork/security-advisory/cpujul2019-5072835.html
https://www.oracle.com/technetwork/security-advisory/cpuapr2019-5072813.html
https://www.debian.org/security/2019/dsa-4386
https://usn.ubuntu.com/3882-1/
https://security.netapp.com/advisory/ntap-20190315-0001/
https://security.gentoo.org/glsa/201903-03
https://curl.haxx.se/docs/CVE-2019-3823.html
https://cert-portal.siemens.com/productcert/pdf/ssa-936080.pdf
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-3823