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
connections.

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
releases.

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.

net.ipv4.tcp_challenge_ack_limit = 1000000000