CVE-2018-5391: The Linux kernel, versions 3.9+, IP implementation is vulnerable to denial of service conditions with low rates of specially modified packets

Is it exploited?

Reported, not confirmed by CISA. VulnCheck KEV lists it as exploited in the wild. CISA has not added it to its Known Exploited Vulnerabilities catalog as of 29 Oct 2026.

VulnCheck KEV lists it since 25 Feb 2020. It cites 5 public reports, the first from 25 Feb 2020.

• csk.gov.in
• cybersecurityworks.com
• cybersecurityworks.com

How likely is exploitation in the next 30 days?

32.4%

EPSS score, percentile 98.3 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

Not scored

The CVE record carries no CVSS score.

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (12)

Which versions are affected?

Affected

• 3.9

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; VulnCheck KEV, as of 30 Oct 2026; FIRST EPSS, as of 30 Oct 2026; CVE List, as of 30 Oct 2026. About the data.

Description

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

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.

Source: CVE List, as of 30 Oct 2026. About the data.

What to do

Advisories and patches

• RHSA-2018:3540 (Vendor advisory)
• RHSA-2018:2785 (Vendor advisory)
• RHSA-2018:3083 (Vendor advisory)
• RHSA-2018:2925 (Vendor advisory)
• USN-3741-2 (Vendor advisory)
• RHSA-2018:3459 (Vendor advisory)
• RHSA-2018:2933 (Vendor advisory)
• USN-3740-2 (Vendor advisory)
• USN-3741-1 (Vendor advisory)
• RHSA-2018:3590 (Vendor advisory)
• RHSA-2018:2948 (Vendor advisory)
• USN-3742-2 (Vendor advisory)

This summary is based on the CVE record as of 30 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

Source: CVE List, as of 30 Oct 2026. About the data.

Timeline

Known exploited Linux vulnerabilities

• CVE-2026-46300: Linux Kernel Missing Initialization of a Variable Vulnerability (added 28 Oct 2026)
• CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability (added 18 Sep 2026)
• CVE-2025-39964: Linux Kernel Race Condition Vulnerability (added 18 Sep 2026)
• CVE-2026-53266: Linux Kernel Out-of-Bounds Write Vulnerability (added 18 Sep 2026)
• CVE-2026-53362: Linux Kernel Unspecified Vulnerability (added 27 Aug 2026)