What is CVE-2026-63993?

CVE-2026-63993 is a Critical severity Linux kernel vulnerability with a CVSS score of 9.8 out of 10, classified as a Use After Free flaw (CWE-416), affecting Linux kernel versions from 5.9 onward and patched in 5.10.259, 5.15.210, 6.1.176 and others. CVE-2026-63993 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

What is the CVSS score for CVE-2026-63993?

CVE-2026-63993 has a CVSS score of 9.8 out of 10, rated Critical severity. The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Is there a patch available for CVE-2026-63993?

Yes, CVE-2026-63993 has been patched. Fixed versions include 5.10.259, 5.15.210, 6.1.176 and others. If you are running Linux kernel 5.9 or later up to the fix versions, apply the relevant patch for your kernel branch.

Is CVE-2026-63993 actively exploited?

CVE-2026-63993 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

What is Use After Free (CWE-416)?

The product references memory after it has been freed, which may cause it to crash, use unexpected values, or execute code. See MITRE CWE for full details: https://cwe.mitre.org/data/definitions/416.html

CVE-2026-63993

Critical

In the Linux kernel, the following vulnerability has been resolved: vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu() skb_tunnel_check_pmtu() can change skb->head. Reusing old_iph afer skb_tunnel_check_pmtu() can cause an UAF. Use instead ip_hdr(skb) as done in drivers/net/bareudp.c and drivers/net/geneve.c. Found by Sashiko.

Package Linux Kernel

Published 2026-07-19

Last modified 2026-10-16

CVSS version 3.1

Patch available

Yes

CVSS 3.1 score

9.8

out of 10

Critical

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Vector string

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Weakness type

CWE-416

CVE-2026-63993 is a Use After Free vulnerability

What is Use After Free?

The product references memory after it has been freed, which may cause it to crash, use unexpected values, or execute code. Learn more on MITRE CWE

Affected versions

Linux kernel versions 5.9 and later are affected. Fixed in 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, 6.18.35, 7.0.12, 7.1 and their respective stable series.

Affected from

≥ 5.9

Fixed in

✓ 5.10.259 5.10.x ✓ 5.15.210 5.15.x ✓ 6.1.176 6.1.x ✓ 6.6.143 6.6.x ✓ 6.12.93 6.12.x ✓ 6.18.35 6.18.x ✓ 7.0.12 7.0.x ✓ 7.1

References

8 total

Kernel Git
https://git.kernel.org/stable/c/5303925e360527243b46a440a04667826bbc72b7

Patch
Kernel Git
https://git.kernel.org/stable/c/609e63312c29aad18026a1d3222e123d4b6b0feb

Patch
Kernel Git
https://git.kernel.org/stable/c/6b8bfce9d2f774d2c2243e0248e03efb99bba6c0

Patch
Kernel Git
https://git.kernel.org/stable/c/7d9ef0cb271555d8cf39fefe6c981e1493b25ecf

Patch
Kernel Git
https://git.kernel.org/stable/c/8d435d68d71fb875876b722f4136caf74f2f48bd

Patch

Showing 5 of 8 references View all on NVD

Details

CVE ID CVE-2026-63993

Severity Critical

CVSS score 9.8 / 10

CVSS version 3.1

Published 2026-07-19

Modified 2026-10-16

KEV No

Patch

Yes

Package linux

Frequently asked questions

What is CVE-2026-63993?

CVE-2026-63993 is a Critical severity Linux kernel vulnerability with a CVSS score of 9.8 out of 10 , classified as an Use After Free flaw (CWE-416) . It affects Linux kernel versions from 5.9 onward and has been patched in 5.10.259, 5.15.210, 6.1.176 and others. CVE-2026-63993 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.
What is the CVSS score for CVE-2026-63993?

CVE-2026-63993 has a CVSS score of 9.8 out of 10, rated Critical severity (CVSS 3.1). The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
Is there a patch available for CVE-2026-63993?

Yes. CVE-2026-63993 has been patched. Fixed versions include 5.10.259, 5.15.210, 6.1.176 and others. If you are running Linux kernel 5.9 or later up to the fix versions, apply the relevant patch for your kernel branch.
Is CVE-2026-63993 actively exploited?

No. CVE-2026-63993 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.