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McAfee Security Bulletin: Email Gateway 7.6 update fixes a file extension filtering issue (CVE-2016-8005)
Security Bulletins ID:   SB10161
Last Modified:  5/17/2017

Summary

First Published: 6/9/2016
 
 Impact of Vulnerability:  Application Protections Bypass (CWE-592)
 CVE Numbers:  CVE-2016-8005
 Severity Rating:  Medium
 CVSS v3 Base / Temporal Scores:  7.1 / 6.4
 Recommendations:  Install or update to Email Gateway (MEG) 7.6.404 HF128596
 Security Bulletin Replacement:  None
 Affected Software:  MEG 7.6 and earlier
 Location of Updated Software:  http://www.mcafee.com/us/downloads/downloads.aspx

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Article contents:

Description

MEG is vulnerable to file attachments containing the null character. The scanning mechanism fails to identify the file name properly.
 
The fix changes the file name processing functionality to remove NULL characters from the raw header value before it is decoded. This addresses the vulnerability; however, there is still an exploit situation because certain mail clients, such as Microsoft Outlook, use a "." in place of the NULL. Hence, a file name of "test<NUL>vbs" that will now be treated as "testvbs" may be treated as "test.vbs" by the mail client. In such situations you would need to change your File Filter rule from "*.vbs" to just "*vbs" to protect against the exploit.
 
This flaw is encountered when the MEG file filtering process scans an email with a forged attached filename that uses a null byte within the filename extension.

CVE-2016-8005
File extension filtering vulnerability in McAfee Email Gateway (MEG) before 7.6.404h1128596 allows attackers to fail to identify the file name properly via scanning an email with a forged attached filename that uses a null byte within the filename extension.
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-8005
 
Affected Component:
  • Email Gateway 7.6

Remediation

Go to the Product Downloads site and download the applicable product hotfix file. In addition, change the File Filter rule from "*.extension" to just "*extension" to protect against the exploit.
 
Product Type Version File Name Release Date
Email Gateway 7.6 (MEG) Hotfix 7.6.404h1128596 MEG-7.6.404h1128596-3334.102.zip June 7, 2016

Download and Installation Instructions
See KB56057 for instructions on how to download McAfee products, documentation, security updates, patches, and hotfixes. Review the Release Notes and the Installation Guide, which you can download from the Documentation tab, for instructions on how to install these updates.

Workaround

None. McAfee strongly recommends that you install the available hotfix.

Mitigations

No vulnerability detection signatures are available.

Acknowledgements

McAfee credits Thomas Damonneville and Lionel Prat from The French National Health Insurance Fund for Salaried Worker (Caisse nationale de l'assurance maladie des travailleurs salariés / CNAMTS) for reporting this flaw.

Frequently Asked Questions (FAQs)

How do I know whether my McAfee product is vulnerable or not?

For Appliances:
Use the following instructions for Appliance based products:
  1. Open the Administrator's User Interface (UI).
  2. Click the About link. The product version is displayed.
What is CVSS?
CVSS, or Common Vulnerability Scoring System, is the result of the National Infrastructure Advisory Council’s effort to standardize a system of assessing the criticality of a vulnerability. This system offers an unbiased criticality score between 0 and 10 that customers can use to judge how critical a vulnerability is and plan accordingly. For more information, please visit the CVSS website at: http://www.first.org/cvss/.

When calculating CVSS scores, McAfee has adopted a philosophy that fosters consistency and repeatability. Our guiding principle for CVSS scoring is to score the exploit under consideration by itself. We consider only the immediate and direct impact of the exploit under consideration. We do not factor into a score any potential follow-on exploits that might be made possible by successful exploitation of the issue being scored.
 
What are the CVSS scoring metrics that have been used?
 
CVE-2016-8005: File Extension Filtering Vulnerability
 
 Base Score 7.1
 Attack Vector (AV) Network (N)
 Attack Complexity (AC) Low (L)
 Privileges Required (PR) Low (L)
 User Interaction (UI) None (N)
 Scope (S) Unchanged (U)
Confidentiality (C) None (N)
Integrity (I) High (H)
Availability (A) None (N)
 Temporal Score (Overall) 6.4
 Exploitability (E) Proof-of-Concept (P)
 Remediation Level (RL) Official Fix (O)
 Report Confidence (RC) Confirmed (C)

NOTE: The below CVSS version 3.0 vector was used to generate this score.
https://nvd.nist.gov/cvss/v3-calculator?vector=AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N/E:P/RL:O/RC:C

Where can I find a list of all security bulletins or how do I report a product vulnerability?
To find a list of all security bulletins, or if you have information about a security issue or vulnerability with a McAfee product, please visit our product security website at: http://www.mcafee.com/us/threat-center/product-security-bulletins.aspx.

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Disclaimer

The information provided in this security bulletin is provided as is without warranty of any kind. McAfee disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall McAfee or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits, or special damages, even if McAfee or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
 
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