[arch-security] [ASA-201608-13] linux-grsec: information disclosure
rgacogne at archlinux.org
Sun Aug 14 14:25:36 UTC 2016
Arch Linux Security Advisory ASA-201608-13
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
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
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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