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McAfee Security Bulletin: kernel challenge ACK counter information disclosure vulnerability (CVE-2016-5696)
Security Bulletins ID:   SB10167
Last Modified:  10/24/2019


First Published: 8/25/2016
 Impact of Vulnerability:  Denial of Service (CWE-730)
 Predictable from Observable State (CWE-341)
 Predictable Value Range from Previous Values (CWE-343)
 CVE Numbers:  CVE-2016-5696
 Severity Rating:  Medium
 Base / Overall CVSS v3 Scores:  Base: 4.8, Temp: 4.2
 Recommendations: McAfee Web Gateway (MWG): Install or update to or
Threat Intelligence Exchange (TIE) Server: Install or update to 2.0.0 or later.
 Security Bulletin Replacement:  None
 Affected Software:  MWG and earlier, and earlier
TIE Server 1.3.0 and earlier
 Also, see the McAfee Product Vulnerability Status lists below.
 Location of Updated Software:  http://www.mcafee.com/us/downloads/downloads.aspx

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Article contents:


Attackers can by perform a side channel attack on the global challenge ACK counter in the Linux kernel. This allows them to obtain current sequence and ACK values and spoof TCP packets. This can be leveraged to terminate or modify TCP connections.
This vulnerability affects the Linux kernel.
CWE-730 Denial of Service
The attacker can prevent the system from providing its service.
CWE-341 Predictable from Observable State
A number or object is predictable based on observations that the attacker can make about the state of the system or network, such as time, process ID, and so on.
CWE-343 Predictable Value Range from Previous Values
The software's random number generator produces a series of values that, when observed, can be used to infer a relatively small range of possibilities for the next value that could be generated. (In this scenario there is no RNG used, but a fixed value instead, in other words, the attacker does not have to guess this value, but already knows it.)
McAfee Product Vulnerability Status

Investigation into all McAfee products is ongoing. This security bulletin will be updated as additional information is available. Not every version of the “Vulnerable and Updated” products are vulnerable. See the Product Specific Notes section for details. Products not on these lists or on the “No Vulnerabilities Reported” list are being investigated.
Vulnerable and Updated
  1. McAfee Web Gateway (MWG)
  2. Threat Intelligence Exchange (TIE) Server
Vulnerable and Not Yet Updated
  1. GTI Cloud Server
  3. McAfee Security Information and Event Management (SIEM)
  4. SaaS Email Archiving (SaaS Archiving)
  5. SaaS Email Protection and Continuity (SaaS Email)
  6. True Key
Not Vulnerable
  1. Network Security Platform (NSP) Sensor
No Vulnerabilities Reported
  1. Advanced Threat Defense (ATD)
  2. Capture Service (CS)
  3. Cloud Analysis and Deconstruction Service (CADS)
  4. Content Security Reporter (CSR)
  5. Data eXchange Layer (DXL) Framework
  6. Data Loss Prevention Endpoint (DLPe)
  7. Database Activity Monitoring (DAM)
  8. Database Vulnerability Manager (DVM)
  9. Drive Encryption (DE)
  10. Email and Web Security (EWS)
  11. Endpoint Encryption for Files and Folders (EEFF)
  12. Endpoint Encryption for PCs (EEPC) / McAfee Drive Encryption (MDE)
  13. Endpoint Encryption for Removable Media – USB (EERM)
  14. Endpoint Encryption Manager (EEM/SafeBoot)
  15. Endpoint Intelligence Agent (EIA) [End of Life 2015]
  16. Endpoint Protection for Mac (EPM)
  17. Enterprise Mobility Manager (EMM)
  18. ePO Cloud (TPS)
  19. ePO Deep Command (eDC)
  20. ePolicy Orchestrator (ePO)
  21. File and Removable Media Protection (FRP)
  22. Host Data Loss Prevention (HDLP)
  23. Host Intrusion Prevention Services (HIPS)
  24. Management for Optimized Virtual Environments (MOVE) AntiVirus
  25. McAfee Agent (MA)
  26. McAfee Anti-Theft (MAT)
  27. McAfee Application Control (MAC)
  28. McAfee Asset Manager (MAM)
  29. McAfee Change Control (MCC)
  30. McAfee Cloud Single Sign On (MCSSO) / McAfee Cloud Identity Manager (MCIM)
  31. McAfee Email Gateway (MEG) / Email and Web Security (EWS)
  32. McAfee Endpoint Security 10 (ENS)
  33. McAfee Firewall Enterprise (MFE)
  34. McAfee Firewall Enterprise Control Center (MFE CC)
  35. McAfee MOVE AntiVirus Security Virtual Appliance (MOVE SVA)
  36. McAfee MOVE AntiVirus Security Virtual Appliance Manager (MOVE SVA Manager)
  37. McAfee MOVE Firewall (MOVE Firewall)
  38. McAfee Policy Auditor (MPA)
  39. McAfee Quarantine Manager (MQM)
  40. McAfee Real Time for ePO (RTS) [End of Life December 26, 2015]
  41. McAfee Security for Email Servers (MSES)
  42. McAfee Security for Lotus Domino (MSLD) / Domino Windows (MSDW)
  43. McAfee Security for Mac (MSM)
  44. McAfee Security for Microsoft Exchange (MSME)
  45. McAfee Security for Microsoft SharePoint (MSMS)
  46. McAfee Security Management Center (SMC)
  47. McAfee SSL VPN (VPN)
  48. McAfee Vulnerability Manager (MVM)
  49. McAfee Web Gateway (MWG)
  50. McAfee Web Reporter (MWR)
  51. Network Data Loss Prevention (NDLP)
  52. Network Security Manager (NSM)
  53. Network Threat Behavior Analysis (NTBA)
  54. Network Threat Response (NTR)
  55. Next-Generation Firewall (NGFW)
  56. One Time Password (OTP) / Pledge
  57. Public Cloud Security (PCS) [Ships Q2 ‘15]
  58. Rogue System Detection (RSD)    [part of MAM]
  59. SaaS Account Management (SAM)
  60. SaaS Endpoint Protection (SEP)
  61. SaaS Web Protection (SaaS Web)
  62. Site Advisor Enterprise (SAE)
  63. Total Protection Service Client (ToPS)
  64. Virus Scan Enterprise (VSE)
  65. VirusScan Enterprise for Storage (VSES)
  66. VirusScan Enterprise Linux (VSEL)
  67. VirusScan for Mac (VSMac)
  68. Whole Disk Encryption (WDE)
For a description of each product, see: http://www.mcafee.com/us/apps/products-az.aspx.


Go to the Product Downloads site and download the applicable product patch/hotfix files:
Product Type Version File Name Release Date
MWG Maintenance Release n/a August 23, 2016
MWG Maintenance Release n/a August 23, 2016
TIE Server Version update 2.1.1 n/a December 5, 2017

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.

Product Specific Notes

  • MWG
    For more information on the releases, see:
    • PD26663 - Web Gateway Release Notes
    Also, see KB87644 - Web Gateway response to CVE-2016-5696 - Global Rate Limit Exploit (Vulnerable).
  • SIEM
    SIEM/Enterprise Security Manager release 9.6.0 is not vulnerable.


McAfee credits Cao Yue, a Ph.D. student from University of California, Riverside for reporting this flaw at the GeekPwn Macau Contest.

Frequently Asked Questions (FAQs)

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

For Endpoint products:
Use the following instructions for endpoint or client based products:
  1. Right-click on the McAfee tray shield icon on the Windows task bar.
  2. Select Open Console.
  3. In the console, select Action Menu.
  4. In the Action Menu, select Product Details. The product version is displayed.
For ePO:
Check the version and build of ePO that is installed. For information on how to check the version, see KB52634.

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-2016-5696 - kernel: challenge ACK counter information disclosure
 Base Score 4.8
 Attack Vector (AV) Network (N)
 Attack Complexity (AC) High (H)
 Privileges Required (PR) None (N)
 User Interaction (UI) None (N)
 Scope (S) Unchanged (U)
Confidentiality (C) None (N)
Integrity (I) Low (L)
Availability (A) Low (L)
 Temporal Score (Overall) 4.2
 Exploitability (E) Proof of concept Code (P)
 Remediation Level (RL) Official Fix (O)
 Report Confidence (RC) Reasonable (R)

NOTE: The below CVSS version 3.0 vector was used to generate this score.

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.


To contact Technical Support, log on to the ServicePortal and go to the Create a Service Request page at https://support.mcafee.com/ServicePortal/faces/serviceRequests/createSR:
  • If you are a registered user, type your User Id and Password, and then click Log In.
  • If you are not a registered user, click Register and complete the required fields. Your password and logon instructions will be emailed to you.


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.
Any future product release dates mentioned in this security bulletin are intended to outline our general product direction and they should not be relied on in making a purchasing decision. The product release dates are for information purposes only, and may not be incorporated into any contract. The product release dates are not a commitment, promise, or legal obligation to deliver any material, code, or functionality. The development, release, and timing of any features or functionality described for our products remains at our sole discretion and may be changed or cancelled at any time.

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