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Package : linux
CVE ID : CVE-2016-5696 CVE-2016-6136 CVE-2016-6480 CVE-2016-6828

Several vulnerabilities have been discovered in the Linux kernel that
may lead to a privilege escalation, denial of service or have other


Yue Cao, Zhiyun Qian, Zhongjie Wang, Tuan Dao, and Srikanth V.
Krishnamurthy of the University of California, Riverside; and Lisa
M. Marvel of the United States Army Research Laboratory discovered
that Linux's implementation of the TCP Challenge ACK feature
results in a side channel that can be used to find TCP connections
between specific IP addresses, and to inject messages into those

Where a service is made available through TCP, this may allow
remote attackers to impersonate another connected user to the
server or to impersonate the server to another connected user. In
case the service uses a protocol with message authentication
(e.g. TLS or SSH), this vulnerability only allows denial of
service (connection failure). An attack takes tens of seconds, so
short-lived TCP connections are also unlikely to be vulnerable.

This may be mitigated by increasing the rate limit for TCP
Challenge ACKs so that it is never exceeded:
    sysctl net.ipv4.tcp_challenge_ack_limit=1000000000


Pengfei Wang discovered that the audit subsystem has a
'double-fetch' or 'TOCTTOU' bug in its handling of special
characters in the name of an executable. Where audit logging of
execve() is enabled, this allows a local user to generate
misleading log messages.


Pengfei Wang discovered that the aacraid driver for Adaptec RAID
controllers has a 'double-fetch' or 'TOCTTOU' bug in its
validation of 'FIB' messages passed through the ioctl() system
call. This has no practical security impact in current Debian


Marco Grassi reported a 'use-after-free' bug in the TCP
implementation, which can be triggered by local users. The
security impact is unclear, but might include denial of service or
privilege escalation.

For the stable distribution (jessie), these problems have been fixed in
version 3.16.36-1+deb8u1. In addition, this update contains several
changes originally targeted for the upcoming jessie point release.

For vyos 1.2+ these should be fixed by just updating image to upstream.
For vyos 1.0 - one should fix procps package by adding

net.ipv4.tcp_challenge_ack_limit = 1000000000

line to /etc/sysctl.conf


Difficulty level
Easy (less than an hour)

Event Timeline

syncer raised the priority of this task from High to Unbreak Now!.
syncer edited projects, added VyOS 1.1.x; removed VyOS 1.1.x (1.1.8).
syncer added subscribers: dmbaturin, syncer.

@dmbaturin is this good reason for 1.1.8 ?

Anything local should hardly be considered high priority, but the first one is remote. We definitely should include the fix in the 1.1.8

Though, since it can be mitigated on live systems easily, I don't think it should trigger immediate release of 1.1.8 with it (i.e. not necessarily today ;). There are some fixes we may want to backport. I'll make a blog post with a guideline for fixing it on live systems.

syncer lowered the priority of this task from Unbreak Now! to High.Nov 5 2016, 1:01 PM
syncer edited projects, added VyOS 1.1.x (1.1.8); removed VyOS 1.1.x, VyOS 2.0.x.
syncer set Version to -.
syncer added a project: VyOS 1.2 Crux.
syncer edited subscribers, added: Maintainers; removed: syncer, dmbaturin.
syncer added a subscriber: dmbaturin.

Please check when you have time for 1.1.8

syncer changed the edit policy from "Public (No Login Required)" to "Custom Policy".Aug 21 2017, 2:25 AM
syncer added subscribers: UnicronNL, higebu.

@UnicronNL can you add

net.ipv4.tcp_challenge_ack_limit = 1000000000

to default systctl.conf

I've just sent a pull-request related for this topic.
Please check them when you have time.

syncer moved this task from Need Triage to Finished on the VyOS 1.2 Crux board.