Commit 5a285a4d authored by Lars Ingebrigtsen's avatar Lars Ingebrigtsen

Make more TLS checks trigger on the default `medium' level

* doc/emacs/misc.texi (Network Security): Update the doc to say
what's on the different levels.

* lisp/net/nsm.el (nsm-protocol-check--intermediary-sha1): Check
intermediary certificates for SHA1.
(nsm-protocol-check--3des): Check for 3DES ciphers.
(network-security-protocol-checks): Put most of the checks on
`medium'.
parent fea8c7d1
......@@ -352,19 +352,6 @@ over these connections. Similarly, if you're sending email via
connection to be encrypted. If the connection isn't encrypted,
@acronym{NSM} will warn you.
@end table
If @code{network-security-level} is @code{high}, the following checks
will be made, in addition to the above:
@table @asis
@item a validated certificate changes the public key
Servers change their keys occasionally, and that is normally nothing
to be concerned about. However, if you are worried that your network
connections are being hijacked by agencies who have access to pliable
Certificate Authorities which issue new certificates for third-party
services, you may want to keep track of these changes.
@item Diffie-Hellman low prime bits
When doing the public key exchange, the number of prime bits
should be high to ensure that the channel can't be eavesdropped on by
......@@ -374,10 +361,34 @@ third parties. If this number is too low, you will be warned.
The @acronym{RC4} stream cipher is believed to be of low quality and
may allow eavesdropping by third parties.
@item @acronym{SHA1} in the host certificate or in intermediary certificates
It is believed that if an intermediary certificate uses
the @acronym{SHA1} hashing algorithm, then third parties can issue
certificates pretending to be that issuing instance. These
connections are therefore vulnerable to man-in-the-middle attacks.
@item @acronym{SSL1}, @acronym{SSL2} and @acronym{SSL3}
The protocols older than @acronym{TLS1.0} are believed to be
vulnerable to a variety of attacks, and you may want to avoid using
these if what you're doing requires higher security.
@end table
If @code{network-security-level} is @code{high}, the following checks
will be made, in addition to the above:
@table @asis
@item @acronym{3DES} cipther
The @acronym{RC4} stream cipher is believed by some to be of low
quality and may allow eavesdropping by third parties.
@item a validated certificate changes the public key
Servers change their keys occasionally, and that is normally nothing
to be concerned about. However, if you are worried that your network
connections are being hijacked by agencies who have access to pliable
Certificate Authorities which issue new certificates for third-party
services, you may want to keep track of these changes.
@end table
Finally, if @code{network-security-level} is @code{paranoid}, you will
......
......@@ -135,6 +135,10 @@ the data.
of what checks to run via the `network-security-protocol-checks'
variable.
+++
** Most of the checks for outdated, believed-to-be-weak TLS algorithms
and ciphers are now switched on by default.
+++
** New function 'fill-polish-nobreak-p', to be used in 'fill-nobreak-predicate'.
It blocks line breaking after a one-letter word, also in the case when
......
......@@ -182,10 +182,12 @@ unencrypted."
process))))))
(defvar network-security-protocol-checks
'((diffie-hellman-prime-bits high 1024)
(rc4 high)
(signature-sha1 high)
(ssl high))
'((diffie-hellman-prime-bits medium 1024)
(rc4 medium)
(signature-sha1 medium)
(intermediary-sha1 medium)
(3des high)
(ssl medium))
"This variable specifies what TLS connection checks to perform.
It's an alist where the first element is the name of the check,
the second is the security level where the check kicks in, and the
......@@ -230,6 +232,13 @@ HOST PORT STATUS OPTIONAL-PARAMETER.")
"The Diffie-Hellman prime bits (%s) used for this connection to %s:%s is less than what is considered safe (%s)."
prime-bits host port bits))))
(defun nsm-protocol-check--3des (host port status _)
(or (not (string-match "\\b3DES\\b" (plist-get status :cipher)))
(nsm-query
host port status :rc4
"The connection to %s:%s uses the 3DES cipher (%s), which is believed to be unsafe."
host port (plist-get status :cipher))))
(defun nsm-protocol-check--rc4 (host port status _)
(or (not (string-match "\\bRC4\\b" (nsm--encryption status)))
(nsm-query
......@@ -246,6 +255,21 @@ HOST PORT STATUS OPTIONAL-PARAMETER.")
"The certificate used to verify the connection to %s:%s uses the SHA1 algorithm (%s), which is believed to be unsafe."
host port signature-algorithm))))
(defun nsm-protocol-check--intermediary-sha1 (host port status _)
;; We want to check all intermediary certificates, so we skip the
;; first, reverse the list and then skip the first again, so we miss
;; the first and final certificates in the chain.
(cl-loop for certificate in (cdr (reverse
(cdr (plist-get status :certificates))))
for algo = (plist-get certificate :signature-algorithm)
when (and (string-match "\\bSHA1\\b" algo)
(not (nsm-query
host port status :signature-sha1
"An intermediary certificate used to verify the connection to %s:%s uses the SHA1 algorithm (%s), which is believed to be unsafe."
host port algo)))
do (cl-return nil)
finally (cl-return t)))
(defun nsm-protocol-check--ssl (host port status _)
(let ((protocol (plist-get status :protocol)))
(or (not protocol)
......
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