2010-07-23 12:31:25 +00:00
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Realloc Bug with X.509 certificates in GnuPG
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==============================================
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2010-07-23
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Summary
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=======
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While trying to import a server certificate for a CDN service, a segv
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bug was found in GnuPG's GPGSM tool. It is likely that this bug is
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exploitable by sending a special crafted signed message and having a
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user verify the signature.
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[ Please do not send private mail in response to this message. The
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mailing list gnupg-devel is the best place to discuss this problem
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(please subscribe first so you don't need moderator approval [1]). ]
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Impact
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======
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All applications using GnuPG's GPGSM tool to process S/MIME messages
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or manage X.509 certificates are affected. The bug exists in all
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versions of GnuPG including the recently released GnuPG 2.0.16.
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2010-07-23 16:16:14 +00:00
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GPG (i.e. OpenPGP) is NOT affected.
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GnuPG 1.x is NOT affected because it does not come with the GPGSM
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2010-07-23 12:31:25 +00:00
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tool.
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An exploit is not yet known but it can't be ruled out for sure that
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the problem has not already been identified by some dark forces.
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Description
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===========
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Importing a certificate with more than 98 Subject Alternate Names [2]
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via GPGSM's import command or implicitly while verifying a signature
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causes GPGSM to reallocate an array with the names. The bug is that
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the reallocation code misses assigning the reallocated array to the
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old array variable and thus the old and freed array will be used.
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Usually this leads to a segv.
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It might be possible to use one of the techniques to exploit
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assignments to malloced and freed memory. Such an exploit won't be
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easy to write because the attack vector must fit into a valid ASN.1
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DER encoded DN. To further complicate the task, that DN is not used
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directly but after a transformation to RFC-2253 format.
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Solution
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========
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Apply the following patch. The patch is required for all GnuPG
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versions < 2.0.17. It applies to 2.0.16 but should apply to many
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older versions as well.
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--- kbx/keybox-blob.c (revision 5367)
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+++ kbx/keybox-blob.c (working copy)
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@@ -898,6 +898,7 @@
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rc = gpg_error_from_syserror ();
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goto leave;
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}
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+ names = tmp;
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}
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names[blob->nuids++] = p;
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if (!i && (p=x509_email_kludge (p)))
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Support
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=======
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g10 Code GmbH [3], a Duesseldorf based company owned and headed by
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GnuPG's principal author, is currently funding GnuPG development.
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Support contracts or other financial backing will greatly help us to
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improve the quality of GnuPG.
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Thanks
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======
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Peter Gutmann for his "A mighty fortress is our PKI" mail to the
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cryptography ML which contained a pointer to a certificate to exhibit
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the problem. This bug was created, found and fixed by Werner Koch.
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[1] See http://lists.gnupg.org/mailman/listinfo/gnupg-devel
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[2] <http://cvs.gnupg.org/cgi-bin/viewcvs.cgi/*checkout*/trunk/tests/samplekeys/cert-with-117-akas.pem>
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[3] See http://www.gnupg.org/service.html
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