Re: CVE request: ntp-keygen may generate non-random symmetric keys on big-endian systems

[cve-assign () mitre org]

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> * [Bug 2797] ntp-keygen trapped in endless loop for MD5 keys on big-endian machines.
> https://bugs.ntp.org/show_bug.cgi?id=2797
>
> Patch: http://bk1.ntp.org/ntp-stable/?PAGE=patch&REV=55199296N2gFqH1Hm5GOnhrk9Ypygg

> While the endless loop is not a security flaw per se

The unstated rationale here seems to be "ntp-keygen is a command-line
program that is not normally exposed in a way that crosses privilege
boundaries."

The documentation mentions:

  After setting up the environment it is advisable to update certificates
  from time to time, if only to extend the validity interval.
  Simply run
  @code{ntp-keygen}
  with the same flags as before to generate new certificates

It seems plausible that some sites may have created a web interface so
that operations staff can occasionally do a certificate update (maybe
with a new key), but these staff don't have login access to the
machine running NTP. The flaw would give them the new ability to
(sometimes) launch a CPU consumption attack. However, we have not
actually heard of anyone with a web-based ntp-keygen arrangement, so
we currently don't want to assign a CVE ID for that.

> the fact that
> ntp-keygen generates non-random keys is. If the lowest byte of the temp
> variable happens to be between 0x20 and 0x7f and not #, the generated
> MD5 key will consist of 20 identical characters, meaning only 93
> possible keys can be generated.

Use CVE-2015-3405 for this code error that results in a key space
that's much smaller than expected.

- -- 
CVE assignment team, MITRE CVE Numbering Authority
M/S M300
202 Burlington Road, Bedford, MA 01730 USA
[ PGP key available through http://cve.mitre.org/cve/request_id.html ]
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