Debian 10: DLA-3719-1 critical: phpseclib Remote Access Risk

The SSH transport protocol with certain OpenSSH extensions, allows
remote attackers to bypass integrity checks such that some packets are
omitted (from the extension negotiation message), and a client and
server may consequently end up with a connection for which some security
features have been downgraded or disabled, aka a Terrapin attack. This
occurs because the SSH Binary Packet Protocol (BPP), implemented by
these extensions, mishandles the handshake phase and mishandles use of
sequence numbers. For example, there is an effective attack against
SSH's use of ChaCha20-Poly1305 (and CBC with Encrypt-then-MAC).

For Debian 10 buster, this problem has been fixed in version
1.0.19-3~deb10u2.

We recommend that you upgrade your phpseclib packages.

For the detailed security status of phpseclib please refer to
its security tracker page at:
https://security-tracker.debian.org/tracker/source-package/phpseclib

Further information about Debian LTS security advisories, how to apply