Fully updated 2011-09-20 12:07
PROBLEM #1/2 - FIXEDKB2616676 for XP and W2k3 did not blacklist the mostly used certificates with numbers (7) through (11) described below. Last night (2011-09-19) Microsoft issued an update to correct this.
PROBLEM #2/2 - NOT YET FIXED (MAY AFFECT DUCTH GOVERNMENTAL AND HEALTHCARE PC's)Microsoft may have initially distributed two
additional "DigiNotar Root CA" certificates somewhere between 2005 and May 2007 that have not been rendered untrusted by any of the current Microsoft updates. Furthermore, these certificates may have been included in various software packages. One or both of these root certificates
may still be present in the Windows certificate store. If so, they pose a risk!
I found these certificates by downloading the file "rootsupd.exe" indirectly from "Update for Root Certificates [March 2011] (KB931125)" and unpacking it: among others, it contains a file called "delroots.sst" which includes the two old "DigiNotar Root CA" certificates, listed as numbers 12 and 13 below, and I've included these certs (base64 encoded) below as well.
This IS a problem as DigiNotar has frequently reused the same public key in multiple certificates, and the CN (common name) of the root certificate is often identical! This means that, for a specific endpoint-certificates,
multiple certificate paths may validate it.
STATUS 2011-09-20KB2616676 (Automatic Updates since 2011-09-19) currently includes:
(1) DigiNotar Cyber CA (root=CyberTrust) #1/3
(2) DigiNotar Cyber CA (root=CyberTrust) #2/3
(3) DigiNotar Cyber CA (root=CyberTrust) #3/3
(4) DigiNotar Root CA (root=Entrust) #1/2
(5) DigiNotar Root CA (root=Entrust) #2/2
(6) DigiNotar Services 1024 CA (root=Entrust)
(7) DigiNotar PKIoverheid CA Organisatie - G2 (root=Staat der Nederlanden Organisatie CA - G2)
(8) DigiNotar PKIoverheid CA Overheid (root=Staat der Nederlanden Overheid CA)
(9) DigiNotar PKIoverheid CA Overheid en Bedrijven (root=Staat der Nederlanden Overheid CA)
(10) DigiNotar Root CA #3/4
(11) DigiNotar Root CA G2
Old root certs (from "KB931125/rootsupd.exe/delroots.sst") that
may be present in any of the Windows
trusted certificate stores:
(12) DigiNotar Root CA #1/4 (Possibly removed by Microsoft)
(13) DigiNotar Root CA #2/4 (Possibly removed by Microsoft)
CONSEQUENCEAny PC that happens to include one of the older "DigiNotar Root CA" root certificates in their trusted certificate substores will not by fully protected. Spoofing of https websites may not be detected, and both code and e-mails may have falsified digital signatures which may lead to unjustified trust in the signer.
FIX (FOR NOW)- Be sure to run Microsoft Update (visit
https://www.update.microsoft.com/ when in doubt).
- Check which of the certificates mentioned are in the "Untrusted Certificates" store on your PC. At least DigiNotar certificates (1) through (11) should be present (blacklisted).
- If certificate (12) or (13) is present in any of the
trusted certificate substores, either remove them, or save and manually import them into the
Untrusted certificate substore. Make sure that you perform this task as Administrator (or any other account that is a member of the local Administrators group), and ensure that you import these certificates in the "Local Computer" subsection of "Untrusted Certificates", such that they end up in the registry under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\Disallowed\Certificates (note: the subkeys shown there are identical to the thumbprints of the certificates).
Note: Microsoft informed me that the latest "Update for Root Certificates [June 2011]" (offered as an optional update on
https://www.update.microsoft.com/) should remove certificates (12) and (13) if they happen to be installed. However, during my tests (before and last night) this did not take place (12) and (13) remained in place and were still trusted). Instead,
another DigiNotar root certificate (11) was added as trusted to my PC. Fortunately with no consequences as that one was already blacklisted by KB2616676.
REFERENCESKB2607712:
http://support.microsoft.com/kb/2607712 (distributed 2011-09-06 except in NL)
KB2616676:
http://support.microsoft.com/kb/2616676 (automatic updates 2011-09-13, corrected 2011-09-19)
KB931125:
http://support.microsoft.com/kb/931125 (Update for Root Certificates)
Please find more details in my contributions below. Note that "Modulus first 24 bytes" refers to the first 24 bytes of the "Public Key". By looking at the last few bytes of each of those, one can easily see which public key is used in multiple certificates.
I'm corresponding with Microsoft Security via e-mail trying to convince them to revoke certificates (12) and (13) as well.