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Microsoft Windows NTLM automatically authenticates via SMB when following a file:// URL

Vulnerability Note VU#672268

Original Release Date: 2015-04-13 | Last Revised: 2017-09-05

Overview

Software running on Microsoft Windows that utilizes HTTP requests can be forwarded to a file:// protocol on a malicious server, which causes Windows to automatically attempt authentication via SMB to the malicious server in some circumstances. The encrypted form of the user's credentials are then logged on the malicious server. This vulnerability is alternatively known as "Redirect to SMB".

Description

CWE-201: Information Exposure Through Sent Data

Many software products use HTTP requests for various features such as software update checking. A malicious user can intercept such requests (such as with a MITM proxy) and use HTTP Redirect to redirect the victim a malicious SMB server. If the redirect is a file:// URL and the victim is running Microsoft Windows, Windows will automatically attempt to authenticate to the malicious SMB server by providing the victim's user credentials to the server. These credentials can then be logged by the malicious server. The credentials are encrypted, but may be "brute-forced" to break the encryption.

The following Windows API functions (available via urlmon.dll) have been identified as being affected:

    • URLDownloadA
    • URLDownloadW
    • URLDownloadToCacheFileA
    • URLDownloadToCacheFileW
    • URLDownloadToFileA
    • URLDownloadToFileW
    • URLOpenStream
    • URLOpenBlockingStream

urlmon uses the wininet library for processing, therefore the affected functionality may be contained within wininet; it is currently not clear where the vulnerability lies. Internet Explorer and the WebBrowser component of .NET have also be reported vulnerable to this SMB redirection. For a longer description with more examples, see Cylance's blog on the issue.

While the HTTP Redirect vector is novel, this type of issue with SMB has been well known for some time. For example, see Aaron Spangler's report from 1997, Steve Birnbaum's report, Paul Ashton's report, and information from Microsoft from 2009. Please see the full list of references at the end of this publication.

Impact

An attacker exploiting this vulnerability may obtain the victim's user credentials in an encrypted format.

Solution

The CERT/CC is currently unaware of a full solution to this problem. However, affected users may consider the following workarounds.

Block outbound SMB

Consider blocking outbound SMB connections (TCP ports 139 and 445) from the local network to the WAN.

Update NTLM group policy

This attack may be mitigated in some circumstances by restricting NTLM via appropriate Group Policy. See reference one and reference two from Microsoft.

Do not use NTLM for authentication by default in applications

Developers should ensure their software complies with appropriate Group Policy and does not use NTLM for authentication by default.

Use a strong password and change passwords frequently

Since the credentials are provided to the attacker in encrypted form, a stronger password may require more time to break the encryption. Changing passwords regularly further deters brute-force attacks against the encryption.

Vendor Information

672268
 
Affected   Unknown   Unaffected

AVG Anti-virus Software

Notified:  March 24, 2015 Updated:  April 01, 2015

Statement Date:   April 01, 2015

Status

  Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Adobe

Notified:  March 24, 2015 Updated:  September 05, 2017

Status

  Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

It has been reported to us that CVE-2017-3085 is a form of Redirect to SMB affecting Flash Player. Adobe's security advisory recommends upgrading Flash Player to at least 26.0.0.151, which has addressed the issue.

Vendor References

Microsoft Corporation

Notified:  March 11, 2015 Updated:  April 01, 2015

Status

  Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Oracle Corporation

Notified:  March 24, 2015 Updated:  April 01, 2015

Statement Date:   March 31, 2015

Status

  Affected

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Apple

Notified:  March 24, 2015 Updated:  March 24, 2015

Status

  Unknown

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor References

    Box.com

    Notified:  April 14, 2015 Updated:  April 14, 2015

    Status

      Unknown

    Vendor Statement

    No statement is currently available from the vendor regarding this vulnerability.

    Vendor Information

    We are not aware of further vendor information regarding this vulnerability.

    Addendum

    According to the reporter, the Box Sync client may be vulnerable in certain circumstances if the user accepts an SSL prompt. CERT/CC has been unable to confirm this so far.

    If you have feedback, comments, or additional information about this vulnerability, please send us email.

    COMODO Security Solutions, Inc.

    Notified:  March 24, 2015 Updated:  March 24, 2015

    Status

      Unknown

    Vendor Statement

    No statement is currently available from the vendor regarding this vulnerability.

    Vendor References

      Github

      Updated:  April 13, 2015

      Status

        Unknown

      Vendor Statement

      No statement is currently available from the vendor regarding this vulnerability.

      Vendor Information

      We are not aware of further vendor information regarding this vulnerability.

      Addendum

      The GitHub for Windows installer has been reported to be affected by this vulnerability.

      If you have feedback, comments, or additional information about this vulnerability, please send us email.

      GoPro

      Updated:  April 13, 2015

      Status

        Unknown

      Vendor Statement

      No statement is currently available from the vendor regarding this vulnerability.

      Vendor Information

      We are not aware of further vendor information regarding this vulnerability.

      Addendum

      GoPro Studio has been reported to be affected by this vulnerability.

      If you have feedback, comments, or additional information about this vulnerability, please send us email.

      JetBrains

      Updated:  April 13, 2015

      Status

        Unknown

      Vendor Statement

      No statement is currently available from the vendor regarding this vulnerability.

      Vendor Information

      We are not aware of further vendor information regarding this vulnerability.

      Addendum

      The following software was reported to CERT/CC to be vulnerable; this information has not been verified yet:

      * IntelliJ IDEA
      * PyCharm

      If you have feedback, comments, or additional information about this vulnerability, please send us email.

      Symantec

      Notified:  April 17, 2015 Updated:  April 17, 2015

      Status

        Unknown

      Vendor Statement

      No statement is currently available from the vendor regarding this vulnerability.

      Vendor References

        Unify Inc

        Notified:  April 17, 2015 Updated:  April 17, 2015

        Status

          Unknown

        Vendor Statement

        No statement is currently available from the vendor regarding this vulnerability.

        Vendor References

          View all 12 vendors View less vendors


          CVSS Metrics

          Group Score Vector
          Base 6.3 AV:N/AC:M/Au:S/C:C/I:N/A:N
          Temporal 5.7 E:F/RL:W/RC:C
          Environmental 5.7 CDP:ND/TD:H/CR:ND/IR:ND/AR:ND

          References

          Acknowledgements

          Thanks to Brian Wallace of Cylance, Inc., for reporting this vulnerability.

          This document was written by Garret Wassermann.

          Other Information

          CVE IDs: None
          Date Public: 2015-04-13
          Date First Published: 2015-04-13
          Date Last Updated: 2017-09-05 21:58 UTC
          Document Revision: 66

          Sponsored by the Department of Homeland Security Office of Cybersecurity and Communications.