Integer underflow in Linux kernel - CVE-2026-64009
Published: July 20, 2026
Vulnerability identifier: #VU138639
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-64009
CWE-ID: CWE-191
Exploitation vector: Local access
Exploit availability:
No public exploit available
Vendor: Linux Foundation
Affected software:
Linux kernel
Linux kernel
Detailed vulnerability description
The vulnerability allows a local user to cause a denial of service.
The vulnerability exists due to an integer underflow leading to an out-of-bounds write in the esp component, specifically xfrm_state_mtu(), when processing a UDP datagram through an IPv4 ESP tunnel SA with attacker-controlled parameters. A local user can install a crafted IPv4 ESP tunnel SA and send a UDP datagram through the tunnel to cause a denial of service.
The issue involves a negative length being sign-extended to size_t before being passed to memset() in esp_output_fill_trailer().
How to mitigate CVE-2026-64009
Install security update from vendor's repository.
Sources
- https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93
- https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed
- https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789
- https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90
- https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3
- https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda
- https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2
- https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0