Tag Archives: debugging

Linux TCP SACK Vulnerabilities June 2019

Earlier this week; Netflix’s Cybersecurity team disclosed 3 denial of service vulnerabilities within the Linux kernels (defined) affecting Amazon AWS, Debian, Red Hat, FreeBSD (only 1 vulnerability affects FreeBSD), SUSE and Ubuntu distributions.

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TL DR:
If you use Amazon AWS, Debian FreeBSD, Red Hat, SUSE or Ubuntu, please install the relevant vendor updates or implement the workarounds both linked to below.
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Why should these vulnerabilities be considered important?
All of these vulnerabilities are remotely exploitable. The most serious of which has been given the name “SACK Panic” (CVE-2019-11477) is most likely to be present/enabled in web servers used to run both large and small business or personal websites. Exploiting this issue will lead to your server crashing/becoming unresponsive. It has a CVSS 3 base score of 7.5 (high severity) and with a low complexity for an attacker to leverage.

The second vulnerability CVE-2019-11478 which can cause “SACK Slowness” is also remotely exploitable but is of moderate severity. If an attacker were to create and send a series of SACK packets it can cause the affected Linux systems to use too much resources (both memory and CPU). FreeBSD is vulnerable to a variation of this CVE-2019-5599.

The third and final vulnerability CVE-2019-11479 is again moderate severity causing high resource usage. In this instance; when an attacker would need to set the maximum segment size (MSS) of a TCP connection to it’s smallest limit of 48 bytes and then send a sequence of specially crafted SACK packets.

The name SACK is derived from TCP Selective Acknowledgement (SACK) packets used to speed up TCP re-transmits by informing a sender (in a two-way data transfer) of which data packets have been already been received successfully.

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How can I protect my organisation or myself from these vulnerabilities?
The affected vendors have released updates or workarounds for these vulnerabilities; links to their advisories and recommended actions are provided below.

At this time, it is not known if Apple macOS (which originated from FreeBSD) is affected. It is not mentioned in any of the advisories. Should an advisory be released it will be available from Apple’s dedicated security page.

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Amazon AWS:
https://aws.amazon.com/security/security-bulletins/AWS-2019-005/

Debian:
https://security-tracker.debian.org/tracker/CVE-2019-11477

https://security-tracker.debian.org/tracker/CVE-2019-11478

https://security-tracker.debian.org/tracker/CVE-2019-11479

FreeBSD:
https://github.com/Netflix/security-bulletins/blob/master/advisories/third-party/2019-001/split_limit.patch

RedHat:
https://access.redhat.com/security/vulnerabilities/tcpsack

SUSE:
https://www.suse.com/support/kb/doc/?id=7023928

Ubuntu:
https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/SACKPanic

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Updated: 9th July 2019
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On the 2nd of July 2019; VMware issued some updates for this set of vulnerabilities that affects it’s products. Further updates are pending. If you use any of the following VMware products, please review this security advisory and apply the updates as they become available:

AppDefense
Container Service Extension
Enterprise PKS
Horizon
Horizon DaaS
Hybrid Cloud Extension
Identity Manager
Integrated OpenStack
NSX for vSphere
NSX-T Data Center
Pulse Console
SD-WAN Edge by VeloCloud
SD-WAN Gateway by VeloCloud
SD-WAN Orchestrator by VeloCloud
Skyline Collector
Unified Access Gateway
vCenter Server Appliance
vCloud Availability Appliance
vCloud Director For Service Providers
vCloud Usage Meter
vRealize Automation
vRealize Business for Cloud
vRealize Code Stream
vRealize Log Insight
vRealize Network Insight
vRealize Operations Manager
vRealize Orchestrator Appliance
vRealize Suite Lifecycle Manager
vSphere Data Protection
vSphere Integrated Containers
vSphere Replication

Thank you.

HP audio driver contained keylogger

Late last week it was announced the security firm Swiss security firm ModZero had responsibly disclosed (defined) to HP back in early April 2017 their discovery of an audio driver (Conexant HD Audio) containing a keylogger. The driver is known to be present on 28 HP devices (listed here).

Conexant also creates drivers to Asus, Lenovo and Dell, at this time it is not clear if they use the same driver (security analysts have been unable to discover any other devices using the affected driver).

How can I tell if my HP (or other device) is affected by this vulnerability?
This BleepingComputer article explains how to check for this vulnerability.

Why should this vulnerability be considered important?
The affected audio driver (versions 1.0.0.31 up to and including 1.0.0.46) contained the issue with the issue first being created in December 2015. Thus it has the potential to have gathered a vast quantity of information since this time.

Not only does the driver record key presses (using a low-level keyboard input hook (defined)) but the driver exposes the OutputDebugString and MapViewOfFile APIs (API, defined). The OutputDebugString API enables any running application to capture keystrokes while MapViewOfFile enables any framework or application with access to MapViewOfFile API to do the same.

Since the unencrypted keystrokes are stored in a text file, forensic investigators with access to the log file (stored at C:\Users\Public\MicTray.log) could potentially recover previously saved sensitive data (a reboot or power of the device clears the file). When backups of the affected systems are performed previous versions of this file would contain further captured (and potentially sensitive) information.

Since our keyboards are used to enter all kinds of sensitive information,  emails, chat/instant message conversations, social media posts, credit card numbers etc., this vulnerability could have serious consequences If the log contents were to be obtained by cyber criminals. The file might also contain credentials (usernames/passwords for the above mentioned activities.

From the information disclosed about this vulnerability, there is evidence to suggest the driver uploads/sends the information it gathers within that log to HP, Conexant or anyone else. However if you are creating unencrypted backups within a corporate, small business or consumer environment this file over time will contain more and more information gathered over time. If someone knew you create these backups and knew where to look within them (assuming they are not encrypted), they could gather significant volumes of sensitive information.

How can I protect myself from this vulnerability?
After ModZero disclosed this information to HP, HP made available a driver update (version 10.0.931.90) which removes the keylogging behavior. Moreover, the driver update will be made available via Windows Update for both 2016 and 2015 HP devices. HP Vice President Mike Nash clarified the logging feature of the driver was simply debugging code (defined) inadvertently left within the driver.

If you followed the steps above to check if your device was vulnerable but there is no driver update available, the same BleepingComputer article describes how to mitigate the vulnerability.

Thank you.