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<base href="https://bugs.freedesktop.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Certificate chain from PDF digital signature back to trusted root certificate not verified?"
href="https://bugs.freedesktop.org/show_bug.cgi?id=99365">99365</a>
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<th>Summary</th>
<td>Certificate chain from PDF digital signature back to trusted root certificate not verified?
</td>
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<th>Product</th>
<td>poppler
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
</td>
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<th>Component</th>
<td>general
</td>
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<th>Assignee</th>
<td>poppler-bugs@lists.freedesktop.org
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<th>Reporter</th>
<td>sebras@hotmail.com
</td>
</tr></table>
<p>
<div>
<pre>I believe that the full certificate chain back to a trusted root certificate is
not verified when attempting to verify digital signatures in PDFs.
SignatureHandler::init_nss() initializes NSS to point to my root
certficate database in my firefox profile or if not available
(it is available) /etc/pki/nssdb (which is unpopoulated on my machine).
I believe that the idea is that this database of root certificates
will be used when verifying the chain of certificates in digital signatures.
I downloaded <a href="http://blogs.adobe.com/security/SampleSignedPDFDocument.pdf">http://blogs.adobe.com/security/SampleSignedPDFDocument.pdf</a>
and then ran pdfsig (compiled from git HEAD currently at c301f6c6) like so:
./pdfsig-original ./SampleSignedPDFDocument.pdf
Digital Signature Info of:./SampleSignedPDFDocument.pdf
Signature #1:
- Signer Certificate Common Name: John B Harris
- Signing Time: Jul 16 2009 16:47:47
- Signature Validation: Signature is Valid.
- Certificate Validation: Certificate has Expired
The mesage "Signature is Valid" implies that the chain of certificates
has all been checked. However if I replace the call to NSS_Init() with
a call that explicitlydisables any preinitialized database like so:
diff --git a/poppler/SignatureHandler.cc b/poppler/SignatureHandler.cc
index 15c9321c..4be4a140 100644
--- a/poppler/SignatureHandler.cc
+++ b/poppler/SignatureHandler.cc
@@ -91,16 +91,9 @@ GooString *SignatureHandler::getDefaultFirefoxCertDB_Linux()
*/
void SignatureHandler::init_nss()
{
- GooString *certDBPath = getDefaultFirefoxCertDB_Linux();
- if (certDBPath == NULL) {
- NSS_Init("sql:/etc/pki/nssdb");
- } else {
- NSS_Init(certDBPath->getCString());
- }
+ NSS_NoDB_Init("");
//Make sure NSS root certificates module is loaded
SECMOD_AddNewModule("Root Certs", "libnssckbi.so", 0, 0);
-
- delete certDBPath;
}
And then recompile and rerun pdfsig I get the same message as above:
./pdfsig-changed ./SampleSignedPDFDocument.pdf
Digital Signature Info of: ./SampleSignedPDFDocument.pdf
Signature #1:
- Signer Certificate Common Name: John B Harris
- Signing Time: Jul 16 2009 16:47:47
- Signature Validation: Signature is Valid.
- Certificate Validation: Certificate has Expired
Which again seems to claim that the chain of certificates is valid.
How can that be when there are no trusted root certificates in the database?
This appears to be corroborated by the comment preceeding the function
NSS_CMSSignerInfo_Verify() which SignatureHandler later calls to do the
verification:
"Just verifies the signature. The assumption is that verification of
the certificate is done already", see
<a href="https://hg.mozilla.org/projects/nss/file/tip/lib/smime/cmssiginfo.c#l310">https://hg.mozilla.org/projects/nss/file/tip/lib/smime/cmssiginfo.c#l310</a>
I believe that the intent with the poppler code is to verify
the entire certificate chain (why else bother to add the firefox
root certificate database?), but I don't think that is what is happening.
Unfortunately I'm not yet well versed in this code to figure out
how to fix this, hence there is no patch attached fixing this issue.
Maybe the decision is to be happy that the certificate is self-consistent
and that the digest is matching, etc. but to ignore that the _chain_ of
certificates is never checked, however in that case I'd suggest mentioning
this clearly, e.g. "Signature is Valid (chain back to root certificate not
checked)".
Oh, and of course any UI that uses SignatureHandler is equally affected
as pdfsig, but I find reporting issued using command-line tools easier. :)</pre>
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