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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.

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.

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 Severity Score

4.8

Score breakdown

Status

Package Release Status
linux-armadaxp
Launchpad, Ubuntu, Debian
xenial Does not exist

yakkety Does not exist

zesty Does not exist

precise
Released (3.2.0-1672.98)
trusty Does not exist

wily Does not exist

upstream
Released (4.7)
This package is not directly supported by the Ubuntu Security Team
linux-goldfish
Launchpad, Ubuntu, Debian
zesty Ignored
(end of life)
precise Does not exist

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

trusty Does not exist
(trusty was ignored)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-hwe-edge
Launchpad, Ubuntu, Debian
precise Does not exist

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

zesty Does not exist

trusty Does not exist

upstream
Released (4.7)
linux-linaro-omap
Launchpad, Ubuntu, Debian
precise Ignored
(end of life)
trusty Does not exist

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-linaro-shared
Launchpad, Ubuntu, Debian
precise Ignored
(end of life)
trusty Does not exist

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-linaro-vexpress
Launchpad, Ubuntu, Debian
precise Ignored
(end of life)
trusty Does not exist

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-lts-quantal
Launchpad, Ubuntu, Debian
precise Ignored
(end of life)
trusty Does not exist

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
This package is not directly supported by the Ubuntu Security Team
linux-lts-raring
Launchpad, Ubuntu, Debian
precise Ignored
(end of life)
trusty Does not exist

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-lts-saucy
Launchpad, Ubuntu, Debian
precise Ignored
(end of life)
trusty Does not exist

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
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

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-lts-utopic
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored [end of standard support])
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-lts-vivid
Launchpad, Ubuntu, Debian
precise Does not exist

trusty
Released (3.19.0-68.76~14.04.1)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-lts-wily
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored [end of standard support])
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-lts-xenial
Launchpad, Ubuntu, Debian
precise Does not exist

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

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-maguro
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-mako
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
wily Not vulnerable

xenial Not vulnerable

yakkety Not vulnerable

zesty Does not exist

upstream
Released (4.7)
linux-manta
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
wily Ignored
(end of life)
xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-qcm-msm
Launchpad, Ubuntu, Debian
precise Ignored
(end of life)
trusty Does not exist

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux-raspi2
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

wily Ignored
(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)
upstream
Released (4.7)
linux-snapdragon
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

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)
upstream
Released (4.7)
linux-ti-omap4
Launchpad, Ubuntu, Debian
precise
Released (3.2.0-1487.114)
trusty Does not exist

wily Does not exist

xenial Does not exist

yakkety Does not exist

zesty Does not exist

upstream
Released (4.7)
linux
Launchpad, Ubuntu, Debian
precise
Released (3.2.0-109.150)
trusty
Released (3.13.0-95.142)
wily Ignored
(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)
upstream
Released (4.7)
Patches:
Introduced by

282f23c6ee343126156dd41218b22ece96d747e3

Fixed by 75ff39ccc1bd5d3c455b6822ab09e533c551f758
linux-flo
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist
(trusty was ignored)
wily Not vulnerable

xenial Not vulnerable

yakkety Not vulnerable

zesty Does not exist

upstream
Released (4.7)
linux-aws
Launchpad, Ubuntu, Debian
precise Does not exist

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

zesty Does not exist

upstream
Released (4.7)
linux-gke
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

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

zesty Does not exist

upstream
Released (4.7)
linux-hwe
Launchpad, Ubuntu, Debian
precise Does not exist

trusty Does not exist

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

zesty Does not exist

upstream
Released (4.7)

Severity score breakdown

Parameter Value
Base score 4.8
Attack vector Network
Attack complexity High
Privileges required None
User interaction None
Scope Unchanged
Confidentiality None
Integrity impact Low
Availability impact Low
Vector CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L