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CVE Request: GnuTLS: GNUTLS-SA-2015-2: MD5-based ServerKeyExchange signature accepted by default


From: Salvatore Bonaccorso <carnil () debian org>
Date: Tue, 5 May 2015 10:47:49 +0200

Hi

I wonder if the following issue in GnuTLS should get a CVE:

http://www.gnutls.org/security.html#GNUTLS-SA-2015-2

Karthikeyan Bhargavan reported that a ServerKeyExchange signature
sent by the server is not verified to be in the acceptable by the
client set of algorithms. That has the effect of allowing MD5
signatures (which are disabled by default) in the ServerKeyExchange
message. It is not believed that this bug can be exploited because a
fraudulent signature has to be generated in real-time which is not
known to be possible. However, since attacks can only get better it
is recommended to update to a GnuTLS version which addresses the
issue.

Details: 
https://lists.gnupg.org/pipermail/gnutls-devel/2015-April/007572.html
https://bugzilla.redhat.com/show_bug.cgi?id=1218426

https://lists.gnupg.org/pipermail/gnutls-devel/2015-May/007577.html
https://lists.gnupg.org/pipermail/gnutls-devel/2015-May/007578.html

Upstream commit:
https://gitlab.com/gnutls/gnutls/commit/7d9d5c61f8445dc9e9ca47bb575c77cef17da17a

Testcase:
https://gitlab.com/gnutls/gnutls/commit/6822a37947d4e38c45b1afc0121cda35ba897182

Regards,
Salvatore


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