CVE-2026-63925

Description

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).

References

• https://git.kernel.org/stable/c/23c0e230eab397d7f68be2538790ac41d3bb91fd
• https://git.kernel.org/stable/c/679e13a65e68a67c8b3c0467c02ee89157ec6f0f
• https://git.kernel.org/stable/c/6d00f5c7e5ff7ec4795b7f5f8ed88bd346641652
• https://git.kernel.org/stable/c/79495a1b0944fe31ffd54b54b00211b493590d62
• https://git.kernel.org/stable/c/d15130461df388136b62a7b0ce9f66e7e2fa9ff1