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CVE-2026-45952: eth: fbnic: Add validation for MTU changes

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-27 · updated 2026-06-17

Description

In the Linux kernel, the following vulnerability has been resolved: eth: fbnic: Add validation for MTU changes Increasing the MTU beyond the HDS threshold causes the hardware to fragment packets across multiple buffers. If a single-buffer XDP program is attached, the driver will drop all multi-frag frames. While we can't prevent a remote sender from sending non-TCP packets larger than the MTU, this will prevent users from inadvertently breaking new TCP streams. Traditionally, drivers supported XDP with MTU less than 4Kb (packet per page). Fbnic currently prevents attaching XDP when MTU is too high. But it does not prevent increasing MTU after XDP is attached.

Affected products

• Linux kernel: from 6.18 before 6.18.14; from 6.19 before 6.19.4 — fixed in 6.18.14, 6.19.4

How to fix

Upgrade to a fixed version: Linux kernel 6.18.14, 6.19.4. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/03399063aa0c67fd8bdfd69467ddb849bb3b97df
• https://git.kernel.org/stable/c/ccd8e87748ad083047d6c8544c5809b7f96cc8df
• https://git.kernel.org/stable/c/d7eaa006c0444a5d4671be7efe6dbb33ef8b515e

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