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Posted to bugs@httpd.apache.org by bu...@apache.org on 2016/02/29 02:44:39 UTC
[Bug 59087] New: DH parameters with too small prime lengths used
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
Bug ID: 59087
Summary: DH parameters with too small prime lengths used
Product: Apache httpd-2
Version: 2.4.10
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P2
Component: mod_ssl
Assignee: bugs@httpd.apache.org
Reporter: bjoern@j3e.de
mod_ssl is supposed to use dynamic DH parameter prime lengths. According to the
mod_ssl docs it "hands them out to clients based on the length of the
certificate's RSA/DSA key".
With a configuration with a 2560 bit RSA key, the DH parameter size is 3072
bits, which is fine.
After adding a second ECC certificate with 256 bits to the server, then the
calculation of the DH parameter size for RSA connections fails. With the
additional ECC key installed mod_ssl will use only 1024 bits for DH the
parameters for RSA connections.
For example
TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x9f) DH 3072 bits FS
will be
TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x9f) DH 1024 bits FS WEAK
after adding the additional ECC certificate to the server.
Only the key size of the RSA cert should be used for the calculation of the DH
parameter size of RSA key based connections.
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[Bug 59087] DH parameters with too small prime lengths used
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
--- Comment #1 from Yann Ylavic <yl...@gmail.com> ---
With OpenSSL < 1.0.2, the RSA certificate should be declared last in the
SSLCertificateFile, due to a restriction on the way to retrieve the currently
used certificate/key for these versions.
With OpenSSL >= 1.0.2, it should work out of the box, though.
Which version are you using?
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[Bug 59087] DH parameters with too small prime lengths used
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
--- Comment #4 from Micha Lenk <mi...@lenk.info> ---
So, what is your bug report about? Is it about Ubuntu 14.04 shipping a slightly
outdated version of Apache and OpenSSL?
What could be done by the Apache httpd project regarding your issue?
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[Bug 59087] DH parameters with too small prime lengths used
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
--- Comment #5 from Björn Jacke <bj...@j3e.de> ---
this is for people who read this to know that this workaround does not work for
those versions. Don't get upset about that extra information here. Of course
you cannot fix ubuntu's version, you can only fix the future versions, as
written comment #2.
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[Bug 59087] DH parameters with too small prime lengths used
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
Yann Ylavic <yl...@gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|NEW |RESOLVED
--- Comment #6 from Yann Ylavic <yl...@gmail.com> ---
(In reply to Björn Jacke from comment #5)
> Of course you cannot fix ubuntu's version, you can only fix the future
> versions, as written comment #2.
Unfortunately we can't because openssl < 1.0.2 lacks support for selecting the
current certificate when multiple ones are configured for the same context.
This was added in openssl-1.0.2, and the workaround for earlier versions is the
only way...
I'm marking this PR as invalid, I see no better resolution choice (e.g.
CANTFIX).
Thanks for testing (informing about) the workaround.
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[Bug 59087] DH parameters with too small prime lengths used
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
--- Comment #2 from Björn Jacke <bj...@j3e.de> ---
this is openssl 1.0.1k. Apache/openssl/mod_ssl from current Debian Jessie.
I can confirm that configuring the RSA cert after the ECC makes the DH
parameter size calculation reasonable again. This isn't documented anywhere, is
it? It would also be nice if the oder of certs given would not have such
security related consequences as this configuration to do is not obvious to do
at all. mod_ssl should rather just choose the right parameter size for a RSA
cert and ignore the ECC one for the calculation of that, shouldn't it?
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[Bug 59087] DH parameters with too small prime lengths used
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
--- Comment #7 from Eric Covener <co...@gmail.com> ---
(In reply to Yann Ylavic from comment #6)
> (In reply to Björn Jacke from comment #5)
> > Of course you cannot fix ubuntu's version, you can only fix the future
> > versions, as written comment #2.
>
> Unfortunately we can't because openssl < 1.0.2 lacks support for selecting
> the current certificate when multiple ones are configured for the same
> context.
>
> This was added in openssl-1.0.2, and the workaround for earlier versions is
> the only way...
>
> I'm marking this PR as invalid, I see no better resolution choice (e.g.
> CANTFIX).
> Thanks for testing (informing about) the workaround.
move to DOCS maybe to capture it? I didn't follow too closely.
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[Bug 59087] DH parameters with too small prime lengths used with
openssl < 1.0.2
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
Yann Ylavic <yl...@gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Summary|DH parameters with too |DH parameters with too
|small prime lengths used |small prime lengths used
| |with openssl < 1.0.2
Assignee|bugs@httpd.apache.org |docs@httpd.apache.org
Resolution|INVALID |---
Component|mod_ssl |Documentation
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[Bug 59087] DH parameters with too small prime lengths used
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=59087
--- Comment #3 from Björn Jacke <bj...@j3e.de> ---
on Ubuntu 14.04 systems for example which have Apache 2.4.7 and openssl 1.0.1f
even the order of the rsa/ec certs does *not* change anything. The DH param
length will always be just 1024 bits there.
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