CVE-2026-63925

About vulnerability

In the Linux kernel, the following vulnerability has been resolved:

macsec: fix replay protection at XPN lower-PN wrap

In macsec_post_decrypt(), when pn is U32_MAX, pn + 1 overflows u32 to 0 and the first branch never fires. If next_pn_halves.lower is also in the upper half, pn_same_half(pn, lower) is true and the XPN else-if does not fire either, leaving next_pn_halves unchanged. An attacker that captures the legitimate frame carrying pn == 0xFFFFFFFF on an XPN association can then replay it indefinitely, since lowest_pn never rises above the captured pn and macsec_decrypt() reconstructs the same IV.

Extend the XPN else-if to also fire when pn + 1 wraps to 0, so receipt of pn == U32_MAX advances next_pn_halves to (upper + 1, 0).

Affected product:

AlmaLinux 9.2 ESU , Amazon Linux 2 ELS , TuxCare 9.6 ESU , TuxCare 9.8 ESU , Ubuntu 20.04 ELS

Affected packages:

kernel @ 5.10.0 (+4 more)

Live-patch status from KernelCare for each operating system.