Vulnerability Note VU#641765

Linux kernel IP fragment re-assembly vulnerable to denial of service

Original Release date: 14 Aug 2018 | Last revised: 14 Sep 2018


The Linux kernel, versions 3.9+, IP implementation is vulnerable to denial of service conditions with low rates of specially modified packets.


CWE-400: Uncontrolled Resource Consumption ('Resource Exhaustion') - CVE-2018-5391

The Linux kernel, versions 3.9+, is vulnerable to a denial of service attack with low rates of specially modified packets targeting IP fragment re-assembly. An attacker may cause a denial of service condition by sending specially crafted IP fragments.

Various vulnerabilities in IP fragmentation have been discovered and fixed over the years. The current vulnerability (CVE-2018-5391) became exploitable in the Linux kernel with the increase of the IP fragment reassembly queue size.


An attacker may be able to trigger a denial-of-service condition against the system.


Apply a patch
Patches are available from OS vendors to address the vulnerability.

If you are unable to apply a patch, see the following mitigations:

Modify Default Configurations
Change the (default) values of net.ipv4/ipv6.ipfrag_high_thresh and net.ipv4/ipv6.ipfrag_low_thresh back to 256kB and 192 kB (respectively) or below.

sysctl -w net.ipv4.ipfrag_low_thresh=196608
sysctl -w net.ipv4.ipfrag_high_thresh=262144
sysctl -w net.ipv6.ip6frag_low_thresh=196608
sysctl -w net.ipv6.ip6frag_high_thresh=262144

Further testing shows that these mitigations are not a 100% fix. A significantly strong attack will still result in a denial of service condition.

Revert Commit
Another sufficient mitigation is to revert the commit c2a936600f78aea00d3312ea4b66a79a4619f9b4

Vendor Information (Learn More)

VendorStatusDate NotifiedDate Updated
Arista Networks, Inc.Affected13 Aug 201815 Aug 2018
Check Point Software TechnologiesAffected13 Aug 201813 Sep 2018
Debian GNU/LinuxAffected13 Aug 201815 Aug 2018
Red Hat, Inc.Affected13 Aug 201815 Aug 2018
SUSE LinuxAffected13 Aug 201812 Sep 2018
UbuntuAffected13 Aug 201815 Aug 2018
BroadcomNot Affected13 Aug 201811 Sep 2018
3com IncUnknown13 Aug 201813 Aug 2018
A10 NetworksUnknown13 Aug 201813 Aug 2018
ACCESSUnknown13 Aug 201813 Aug 2018
Actelis NetworksUnknown13 Aug 201813 Aug 2018
ActiontecUnknown13 Aug 201813 Aug 2018
ADTRANUnknown13 Aug 201813 Aug 2018
aep NETWORKSUnknown13 Aug 201813 Aug 2018
AerohiveUnknown13 Aug 201813 Aug 2018
If you are a vendor and your product is affected, let us know.View More »

CVSS Metrics (Learn More)

Group Score Vector
Base 7.8 AV:N/AC:L/Au:N/C:N/I:N/A:C
Temporal 6.6 E:U/RL:ND/RC:ND
Environmental 6.6 CDP:ND/TD:H/CR:ND/IR:ND/AR:ND



Thanks to Juha-Matti Tilli (Aalto University, Department of Communications and Networking / Nokia Bell Labs) for reporting this vulnerability.

This document was written by Trent Novelly.

Other Information

  • CVE IDs: CVE-2018-5391
  • Date Public: 14 Aug 2018
  • Date First Published: 14 Aug 2018
  • Date Last Updated: 14 Sep 2018
  • Document Revision: 29


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