CVE-2021-22947

When curl >= 7.20.0 and <= 7.78.0 connects to an IMAP or POP3 server to
retrieve data using STARTTLS to upgrade to TLS security, the server can
respond and send back multiple responses at once that curl caches. curl
would then upgrade to TLS but not flush the in-queue of cached responses
but instead continue using and trustingthe responses it got before the
TLS handshake as if they were authenticated.Using this flaw, it allows a
Man-In-The-Middle attacker to first inject the fake responses, then
pass-through the TLS traffic from the legitimate server and trick curl into
sending data back to the user thinking the attacker’s injected data comes
from the TLS-protected server.

Notes