CVE-2016-5696

Publication date 6 August 2016

Last updated 25 August 2025

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

4.8 · Medium

Score breakdown

Description

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.

Read the notes from the security team

Mitigation

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

Status

Package Ubuntu Release Status
linux-armadaxp 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise
Fixed 3.2.0-1672.98
linux-goldfish 17.04 zesty Ignored end of life
16.10 yakkety Ignored end of life
16.04 LTS xenial Not in release
15.10 wily Ignored end of life
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-grouper 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-hwe-edge 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-linaro-omap 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Ignored end of life
linux-linaro-shared 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Ignored end of life
linux-linaro-vexpress 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Ignored end of life
linux-lts-quantal 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Ignored end of life
linux-lts-raring 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Ignored end of life
linux-lts-saucy 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Ignored end of life
linux-lts-trusty 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise
Fixed 3.13.0-95.142~precise1
linux-lts-utopic 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-lts-vivid 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty
Fixed 3.19.0-68.76~14.04.1
12.04 LTS precise Not in release
linux-lts-wily 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-lts-xenial 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty
Fixed 4.4.0-36.55~14.04.1
12.04 LTS precise Not in release
linux-maguro 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-mako 17.04 zesty Not in release
16.10 yakkety
Not affected
16.04 LTS xenial Not in release
15.10 wily
Not affected
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-manta 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Ignored end of life
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-qcm-msm 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Ignored end of life
linux-raspi2 17.04 zesty
Not affected
16.10 yakkety
Not affected
16.04 LTS xenial
Fixed 4.4.0-1021.27
15.10 wily Ignored end of life
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-snapdragon 17.04 zesty
Not affected
16.10 yakkety
Not affected
16.04 LTS xenial
Fixed 4.4.0-1024.27
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-ti-omap4 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial Not in release
15.10 wily Not in release
14.04 LTS trusty Not in release
12.04 LTS precise
Fixed 3.2.0-1487.114
linux 17.04 zesty
Not affected
16.10 yakkety
Not affected
16.04 LTS xenial
Fixed 4.4.0-36.55
15.10 wily Ignored end of life
14.04 LTS trusty
Fixed 3.13.0-95.142
12.04 LTS precise
Fixed 3.2.0-109.150
linux-flo 17.04 zesty Not in release
16.10 yakkety
Not affected
16.04 LTS xenial Not in release
15.10 wily
Not affected
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-aws 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial
Not affected
14.04 LTS trusty
Not affected
12.04 LTS precise Not in release
linux-gke 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
12.04 LTS precise Not in release
linux-hwe 17.04 zesty Not in release
16.10 yakkety Not in release
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
12.04 LTS precise Not in release

Notes

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.

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package Patch details
linux

Severity score breakdown

Parameter Value
Base score 4.8 · Medium
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

References

Related Ubuntu Security Notices (USN)

    • USN-3072-2
    • Linux kernel (OMAP4) vulnerabilities
    • 29 August 2016
    • USN-3072-1
    • Linux kernel vulnerabilities
    • 29 August 2016
    • USN-3070-1
    • Linux kernel vulnerabilities
    • 29 August 2016
    • USN-3070-2
    • Linux kernel (Raspberry Pi 2) vulnerabilities
    • 30 August 2016
    • USN-3071-1
    • Linux kernel vulnerabilities
    • 29 August 2016
    • USN-3071-2
    • Linux kernel (Trusty HWE) vulnerabilities
    • 29 August 2016
    • USN-3070-3
    • Linux kernel (Qualcomm Snapdragon) vulnerabilities
    • 30 August 2016
    • USN-3070-4
    • Linux kernel (Xenial HWE) vulnerabilities
    • 30 August 2016

Other references