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Mozilla cleartext credentials leak bug report to excuse myself (Re: NTLM HTTP Authentication is insecure by design - a new writeup by Amit Klein)
Jul 19 2005 08:10PM
3APA3A (3APA3A SECURITY NNOV RU)
Dear Amit Klein (AKsecurity),
--Tuesday, July 19, 2005, 10:22:59 PM, you wrote to 3APA3A (at) SECURITY.NNOV (dot) RU [email concealed]:
AKA> For example, no-one expects NTLM auth to protect data in transit.
Actually, it may with NTLM Session Security.
AKA> Few years ago Internet Explorer was patched to use NTLM
>> authentication only for local network zone. Local network are hosts
>> with NetBIOS name (for example WEBSRV, excluded by default from proxy)
>> and list of proxy exclusions.
AKA> Uh, I don't think so. From my experiments with IE 6.0, it happily engages in NTLM
AKA> authentication on non local network sites. In fact, there are many sites on the Internet
AKA> which require NTLM authentication. For example, OWA 2000/2003...
Yes, sorry, it was my fault. Probably this feature was only implemented
for transparent logon feature of NTLM and I did my tests through a proxy
with NTLM auth disabled.
To excuse myself somehow for the lists I will report security bug
discovered in Mozilla Firefox (Mozilla browser was not tested).
From RFC 2617:
The user agent MUST
choose to use one of the challenges with the strongest auth-scheme it
understands and request credentials from the user based upon that
Instead, Mozilla (tested with Firefox 1.0.4 and 1.0.5 for Windows) uses
authentication schema in the order offered by server. You can test
http://www.security.nnov.ru/files/atest/basic.asp - Basic authentication
http://www.security.nnov.ru/files/atest/digest.asp - Digest authentication
http://www.security.nnov.ru/files/atest/ntlm.asp - NTLM authentication
http://www.security.nnov.ru/files/atest/negotiate.asp - Negotiate authentication
http://www.security.nnov.ru/files/atest/all.asp - Let browser to decide
between above schemas.
Then you visit
with Firefox it becomes clear, that Firefox chooses Basic by default,
digest if basic fails, etc.
It may lead to the leak of the cleartext credentials.
Because this is information leak vulneability and can not be specially
exploited I feel free to report this vulnerability to the lists and
vendor at the same time.
This issue is published as
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