Is CVE-2026-64009 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-64009 being exploited in the wild.

How severe is CVE-2026-64009?

Informational severity, with a CVSS score of 7.8, published 19 July 2026.

Which products and versions are affected?

Linux Kernel c5c252389374 to 742b04d0550b.

Is there a fix for CVE-2026-64009?

A patch was published on 2026-06-19: Patch committed to stable tree Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-64009 attacked?

It is attacked with local access, in an operating system.

Am I affected by CVE-2026-64009?

Check whether you run Linux Kernel at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-64009: Linux Kernel out-of-bounds write in xfrm_state_mtu

CVE-2026-64009 · Severity: info · CVSS 7.8 · Published 2026-07-19

A vulnerability in the Linux kernel's networking component could allow a local user to crash the system or potentially execute unauthorized commands. The issue occurs when processing specific types of encrypted network traffic (IPsec ESP) under unusual configuration settings. By manipulating technical parameters like the Maximum Transmission Unit (MTU) and encryption keys, an attacker can trigger a massive memory corruption event, leading to a complete system failure.

Technologies: Linux Kernel. Vendors: Linux.

Quick answers

Is CVE-2026-64009 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-64009 being exploited in the wild.
How severe is CVE-2026-64009?: Informational severity, with a CVSS score of 7.8, published 19 July 2026.
Which products and versions are affected?: Linux Kernel c5c252389374 to 742b04d0550b.
Is there a fix for CVE-2026-64009?: A patch was published on 2026-06-19: Patch committed to stable tree Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-64009 attacked?: It is attacked with local access, in an operating system.
Am I affected by CVE-2026-64009?: Check whether you run Linux Kernel at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

An integer underflow vulnerability exists in the xfrm_state_mtu() function within the Linux kernel's XFRM (IPsec) subsystem. When calculating the MTU for an ESP tunnel, the function performs unsigned arithmetic that can underflow if the overhead (header length, authentication size, and network adjustment) exceeds the provided MTU. This underflowed value is subsequently treated as a signed integer in esp_output(), resulting in a negative 'tfclen' value. When this negative value is passed to memset() as a size_t, it is sign-extended to a massive positive value, causing an out-of-bounds write of zeroes (approximately 16 exabytes). A local user can trigger this by installing a specific IPv4 ESP tunnel SA with a large authentication key and a small interface MTU. The fix introduces underflow checks in xfrm_state_mtu() to return an error state.

Affected products

Linux Linux Kernel c5c252389374 to 742b04d0550b

Timeline

2026-05-13: other: Patch authored
2026-06-19: patched: Patch committed to stable tree
2026-07-19: disclosed: CVE published

References

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