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Date: Fri, 11 Mar 2016 11:09:54 +0100
From: Hanno Böck <>
Subject: ProFTPD before 1.3.5b/1.3.6rc2 uses 1024 bit Diffie Hellman
 parameters for TLS even if user sets manual parameters


The ProFTPD daemon supports TLS encrypted connections via the mod_tls
module. This module has a configuration option
to specify user-defined Diffie Hellman parameters.

Versions older than 1.3.5b / 1.3.6rc2 had a bug that would cause the
software to ignore the parameters and use Diffie Hellman key exchanges
with 1024 bit:

The release notes[1] are confusing, as they mention only problems with
keys smaller than 2048 bit, but I was also able to reproduce this issue
with 4096 bit keys. But anyway, it is fixed in the latest versions for
all key sizes I have tested.

As 1024 bit DH is considered dangerously small these days and breakable
by a powerful attacker I think this should be considered a security


Hanno Böck


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