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CVE-2016-5696

Published: 6 August 2016

net/ipv4/tcp_input.c in the Linux kernel before 4.7 does not properly determine the rate of challenge ACK segments, which makes it easier for remote attackers to hijack TCP sessions via a blind in-window attack.

From the Ubuntu security team

Yue Cao et al discovered a flaw in the TCP implementation's handling of challenge acks in the Linux kernel. A remote attacker could use this to cause a denial of service (reset connection) or inject content into an TCP stream.

Mitigation

Set the net.ipv4.tcp_challenge_ack_limit sysctl to some absurdly large
number (as described in the lwn article referenced above)
Priority

Medium

CVSS 3 base score: 4.8

Status

Package Release Status
linux
Launchpad, Ubuntu, Debian
precise
Released (3.2.0-109.150)
trusty
Released (3.13.0-95.142)
upstream
Released (4.7)
wily Ignored
(reached end-of-life)
xenial
Released (4.4.0-36.55)
yakkety Not vulnerable
(4.8.0-11.12)
zesty Not vulnerable
(4.8.0-22.24)
Patches:
Introduced by

282f23c6ee343126156dd41218b22ece96d747e3

Fixed by 75ff39ccc1bd5d3c455b6822ab09e533c551f758
linux-armadaxp
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was released [3.2.0-1672.98])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

This package is not directly supported by the Ubuntu Security Team
linux-aws
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Not vulnerable
(4.4.0-1002.2)
upstream
Released (4.7)
xenial Not vulnerable
(4.4.0-1001.10)
yakkety Does not exist

zesty Does not exist

linux-flo
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
upstream
Released (4.7)
wily Not vulnerable

xenial Not vulnerable

yakkety Not vulnerable

zesty Does not exist

linux-gke
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

upstream
Released (4.7)
xenial Not vulnerable
(4.4.0-1003.3)
yakkety Does not exist

zesty Does not exist

linux-goldfish
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
upstream
Released (4.7)
wily Ignored
(reached end-of-life)
xenial Ignored
(abandoned)
yakkety Ignored
(abandoned)
zesty Ignored
(abandoned)
linux-grouper
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-hwe
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

upstream
Released (4.7)
xenial Not vulnerable
(4.8.0-36.36~16.04.1)
yakkety Does not exist

zesty Does not exist

linux-hwe-edge
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

upstream
Released (4.7)
xenial Not vulnerable
(4.8.0-36.36~16.04.1)
yakkety Does not exist

zesty Does not exist

linux-linaro-omap
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was ignored [abandoned])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-linaro-shared
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was ignored [abandoned])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-linaro-vexpress
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was ignored [abandoned])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-lts-quantal
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was ignored [end-of-life])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

This package is not directly supported by the Ubuntu Security Team
linux-lts-raring
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was ignored [end-of-life])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-lts-saucy
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was ignored [end-of-life])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

This package is not directly supported by the Ubuntu Security Team
linux-lts-trusty
Launchpad, Ubuntu, Debian
precise
Released (3.13.0-95.142~precise1)
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-lts-utopic
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored [out of standard support])
upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-lts-vivid
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was released [3.19.0-68.76~14.04.1])
upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-lts-wily
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored [out of standard support])
upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-lts-xenial
Launchpad, Ubuntu, Debian
precise Does not exist

trusty
Released (4.4.0-36.55~14.04.1)
upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-maguro
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-mako
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
upstream
Released (4.7)
wily Not vulnerable

xenial Not vulnerable

yakkety Not vulnerable

zesty Does not exist

linux-manta
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
upstream
Released (4.7)
wily Ignored
(reached end-of-life)
xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-qcm-msm
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was ignored [abandoned])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

linux-raspi2
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

upstream
Released (4.7)
wily Ignored
(reached end-of-life)
xenial
Released (4.4.0-1021.27)
yakkety Not vulnerable
(4.8.0-1012.14)
zesty Not vulnerable
(4.8.0-1013.15)
linux-snapdragon
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial
Released (4.4.0-1024.27)
yakkety Not vulnerable
(4.4.0-1029.32)
zesty Not vulnerable
(4.4.0-1029.32)
linux-ti-omap4
Launchpad, Ubuntu, Debian
precise Does not exist
(precise was released [3.2.0-1487.114])
trusty Does not exist

upstream
Released (4.7)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

Notes

AuthorNote
jdstrand
android kernels (flo, goldfish, grouper, maguro, mako and manta) are
not supported on the Ubuntu Touch 14.10 and earlier preview kernels
linux-lts-saucy no longer receives official support
linux-lts-quantal no longer receives official support
sbeattie
fix is going to land in Ubuntu kernels in this SRU cycle,
with a likely release date of Aug 27. Earlier access to the kernels
with the fix will be available from the -proposed pocket, though they
come with the risk of being less tested.

References