On August 6, 2018, the Vulnerability Coordination team of the National Cyber Security Centre of Finland (NCSC-FI) and the CERT Coordination Center (CERT/CC) disclosed vulnerabilities in the TCP stacks that are used by the Linux and FreeBSD kernels. These vulnerabilities are publicly known as SegmentSmack. The vulnerabilities could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. An attack could be executed by using low transfer rates of TCP packets, unlike typical distributed denial of service (DDoS) attacks. The vulnerabilities are due to inefficient TCP reassembly algorithms in the TCP stacks that are used by the affected kernels. Linux Kernel Versions 4.9 and later and all supported versions of the FreeBSD kernel are known to be affected by these vulnerabilities. An attacker could exploit these vulnerabilities by sending a stream of packets that are designed to trigger the issue in an established TCP session with an affected device. A sustained DoS condition requires the attacker to maintain a continuous stream of malicious traffic. Due to the required use of an established session, an attack cannot be performed using spoofed IP addresses. This advisory is available at the following link: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180824-linux-tcp
On August 6, 2018, the Vulnerability Coordination team of the National Cyber Security Centre of Finland (NCSC-FI) and the CERT Coordination Center (CERT/CC) disclosed vulnerabilities in the TCP stacks that are used by the Linux and FreeBSD kernels. These vulnerabilities are publicly known as SegmentSmack.
The vulnerabilities could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. An attack could be executed by using low transfer rates of TCP packets, unlike typical distributed denial of service (DDoS) attacks.
The vulnerabilities are due to inefficient TCP reassembly algorithms in the TCP stacks that are used by the affected kernels. Linux Kernel Versions 4.9 and later and all supported versions of the FreeBSD kernel are known to be affected by these vulnerabilities.
An attacker could exploit these vulnerabilities by sending a stream of packets that are designed to trigger the issue in an established TCP session with an affected device. A sustained DoS condition requires the attacker to maintain a continuous stream of malicious traffic. Due to the required use of an established session, an attack cannot be performed using spoofed IP addresses.
This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180824-linux-tcp
Cisco investigated its product line to determine which products and services may be affected by these vulnerabilities.
The “Vulnerable Products” section of this advisory includes Cisco bug IDs for each affected product or service. The bugs are accessible through the Cisco Bug Search Tool and contain additional platform-specific information, including workarounds (if available) and fixed software releases.
Any product or service not listed in the “Vulnerable Products” section of this advisory is to be considered not vulnerable.
The following table lists Cisco products that are affected by the Linux Kernel vulnerability that is described in this advisory:
| Product | Cisco Bug ID | Fixed Release Availability |
|---|---|---|
| Network and Content Security Devices | ||
| Cisco Threat Grid Appliance M5 | CSCvk69486 | 2.5 (Oct-2018) |
| Routing and Switching - Enterprise and Service Provider | ||
| Cisco DNA Center | CSCvm34581 | 1.3 (Apr-2019) |
| Cisco Network Assurance Engine | CSCvm34702 | 3.0(0) (Nov-2018) |
| Voice and Unified Communications Devices | ||
| Cisco Webex Hybrid Data Security Node | CSCvm49456 | Cisco will update affected systems (Nov-2018) |
| Cisco Webex Video Mesh Node | CSCvm48163 | Cisco will update affected systems (Nov-2018) |
| Video, Streaming, TelePresence, and Transcoding Devices | ||
| Cisco Expressway Series | CSCvk74922 | x12.5 (Jan-2019) |
| Cisco Meeting Management | CSCvk69487 | 1.1.0.27 (Sept-2018) |
| Cisco TelePresence Conductor | CSCvk75754 | 4.3.4 MR (Nov-2018) |
| Cisco TelePresence Video Communication Server (VCS) | CSCvk74922 | x12.5 (Jan-2019) |
The following table lists Cisco products that are affected by the FreeBSD vulnerability that is described in this advisory:
| Product | Cisco Bug ID | Fixed Release Availability |
|---|---|---|
| Network and Content Security Devices | ||
| Cisco Content Security Management Appliance (SMA) | CSCvk74266 | 12.0.0 (Nov-2018) |
| Cisco Email Security Appliance (ESA) | CSCvk74109 | 11.0.3 (Oct-2018) 12.0.0 (Nov-2018) |
| Cisco Web Security Appliance (WSA) | CSCvk74112 | 10.1.4 (Sept-2018) 10.5.3 (Oct-2018) 11.5.2 (Nov-2018) |
| Video, Streaming, TelePresence, and Transcoding Devices | ||
| Cisco TelePresence MCU 5300 Series, MSE 8510 | CSCvk74254 | 4.5(1.98) (Oct-2018) |
| Cisco TelePresence MCU MSE 8420 | CSCvk74254 | No fix expected - End of life |
| Cisco TelePresence Server 7010 and MSE 8710 | CSCvk74256 | 4.4(1.27) (Dec-2018) |
| Cisco TelePresence Server on Multiparty Media 310, 320 and 820 | CSCvk74256 | 4.4(1.27) (Dec-2018) |
Only products and services listed in the “Vulnerable Products” section of this advisory are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect the following products and services:
Any workarounds will be documented in the product-specific Cisco bugs, which are identified in the “Vulnerable Products” section of this advisory.
It is important to note that exploitation of these vulnerabilities requires an attacker to establish a TCP three-way handshake with an open TCP port on an affected device. Customers are therefore advised to use an external firewall to allow only explicitly trusted source IP addresses to connect to open TCP ports on affected devices.
For information about fixed software releases, consult the Cisco bugs identified in the “Vulnerable Products” section of this advisory.
When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco TAC or their contracted maintenance providers.
The Cisco Product Security Incident Response Team (PSIRT) is not aware of any malicious use of the vulnerabilities that are described in this advisory.
These vulnerabilities were reported by Juha-Matti Tilli, of the Aalto University Department of Communications and Networking, and Nokia Bell Labs.
To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
| Version | Description | Section | Status | Date |
|---|---|---|---|---|
| 1.7 | Updated information about fixed release availability. Removed references to ongoing investigation. | Summary, Affected Products, Vulnerable Products | Final | 2018-November-06 |
| 1.6 | Updated the lists of products under investigation and vulnerable products. | Affected Products, Vulnerable Products | Interim | 2018-September-17 |
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