[manjaro-security] [arch-security] [ASA-201608-13] linux-grsec: information disclosure

Remi Gacogne rgacogne at archlinux.org
Sun Aug 14 16:25:36 CEST 2016

Arch Linux Security Advisory ASA-201608-13

Severity: High
Date    : 2016-08-14
CVE-ID  : CVE-2016-5696
Package : linux-grsec
Type    : information disclosure
Remote  : Yes
Link    : https://wiki.archlinux.org/index.php/CVE


The package linux-grsec before version 4.7.201608131240-1 is vulnerable
to information disclosure.


Upgrade to 4.7.201608131240-1.

# pacman -Syu "linux-grsec>=4.7.201608131240-1"

The problem has been fixed upstream in version 4.7.201608131240.


The challenge ACK rate limiting can be entirely disabled by setting
net.ipv4.tcp_challenge_ack_limit to a very high value. This can be done
by creating a new file in the /etc/sysctl.d/ directory containing the
following line:

net.ipv4.tcp_challenge_ack_limit = 999999999

then issuing the following command so that the new file is taken into

# sysctl --system

Please be aware that this workaround should be removed as soon as a
patched kernel has been installed, as ACK rate limiting is a useful
security feature.


A security issue has been found in the Linux kernel's implementation of
challenge ACKs as specified in RFC 5961. An attacker which knows a
connection's client IP, server IP and server port can abuse the
challenge ACK mechanism to determine the accuracy of a normally 'blind'
attack on the client or server.

Successful exploitation of this flaw could allow a remote attacker to
inject or control a TCP stream contents in a connection between a Linux
device and its connected client/server.


A remote attacker can detect, control and inject content into a TCP stream.



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