High [CVE-2026-63925] fix replay protection at XPN lower-PN wrap
This high-severity Red Hat Linux advisory covers CVE-2026-63925 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Shadow Migration Toolkit for Virtualization for RHEL 10.
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Summary
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).
A flaw was found in the Linux kernel's MACsec (Media Access Control Security) subsystem. When using Extended Packet Numbering (XPN), a vulnerability exists where the replay protection mechanism can be bypassed.
An attacker can exploit an integer overflow when the packet number reaches its maximum value, allowing them to indefinitely replay legitimate MACsec frames. This can lead to a disruption of secure communication and unauthorized re-transmission of data.
Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9; Shadow Migration Toolkit for Virtualization for RHEL 10; Red Hat package: kernel-rt.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · high-confidence parse· fetched 7 days ago·verify at source
- kernel-0:6.12.0-211.65.1.el10_2
- kernel-0:5.14.0-687.57.1.el9_8
- RHSA-2026:81406
- RHSA-2026:81552
Official advisory · high-confidence parse· fetched 7 days ago·verify at source
Mitigation
Upgrade to a fixed release: kernel-0:6.12.0-211.65.1.el10_2, kernel-0:5.14.0-687.57.1.el9_8, RHSA-2026:81406, RHSA-2026:81552. That is the remediation for this advisory.
The vendor advisory may list interim mitigations or workarounds not captured here. Review it before change work.
Official advisory · high-confidence parse· fetched 7 days ago·verify at source
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