VulnerabilityPublished 19 Jul 2026

CVE-2026-63925: Linux kernel · macsec: fix replay protection at XPN lower-PN wrap

Source GCVE Database

Authoritative record:CVE-2026-63925· High 8.1

Not known to be exploited · CVSS 8.1 High · fixed in e68842b3356471ba56c882209f324613dac47f64 : patch Linux kernel soon.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score

8.1High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 28% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in e68842b3356471ba56c882209f324613dac47f64, dd7306779c6ce1238f4cdc34f3c1f2246b854457, d15130461df388136b62a7b0ce9f66e7e2fa9ff1 +5

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Attack Vector: Adjacent
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Adjacent: The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-9hhm-2pf7-p38c

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ a21ecf0e033807b976967286e6c392f48ee2049f, < e68842b3356471ba56c882209f324613dac47f64	Fixed in e68842b3356471ba56c882209f324613dac47f64
LinuxLinux	Affected ≥ a21ecf0e033807b976967286e6c392f48ee2049f, < dd7306779c6ce1238f4cdc34f3c1f2246b854457	Fixed in dd7306779c6ce1238f4cdc34f3c1f2246b854457
LinuxLinux	Affected ≥ a21ecf0e033807b976967286e6c392f48ee2049f, < d15130461df388136b62a7b0ce9f66e7e2fa9ff1	Fixed in d15130461df388136b62a7b0ce9f66e7e2fa9ff1
LinuxLinux	Affected ≥ a21ecf0e033807b976967286e6c392f48ee2049f, < d55acbe577db892b60547b6ef1c020b359331a6d	Fixed in d55acbe577db892b60547b6ef1c020b359331a6d
LinuxLinux	Affected ≥ a21ecf0e033807b976967286e6c392f48ee2049f, < 79495a1b0944fe31ffd54b54b00211b493590d62	Fixed in 79495a1b0944fe31ffd54b54b00211b493590d62
LinuxLinux	Affected ≥ a21ecf0e033807b976967286e6c392f48ee2049f, < 679e13a65e68a67c8b3c0467c02ee89157ec6f0f	Fixed in 679e13a65e68a67c8b3c0467c02ee89157ec6f0f

AI-suggested

A fix for this vulnerability has been implemented in the Linux kernel macsec code. Users should apply the official kernel updates that include this patch. Since no specific patch versions are provided, check the vendor or Linux kernel security advisories for the relevant fixed kernel versions and update accordingly.

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).

Impact

An attacker capable of capturing a legitimate macsec frame with the maximum packet number could replay that frame indefinitely, bypassing replay protection. This undermines the integrity guarantees of macsec by allowing replayed frames to be accepted and decrypted as valid, potentially leading to unauthorized data injection or replay attacks on the protected network traffic.

Summary

The Linux kernel macsec module had a flaw in its replay protection mechanism for Extended Packet Number (XPN) associations. Specifically, when the packet number reaches the maximum 32-bit unsigned integer value (U32_MAX), incrementing it causes an overflow to zero, but the existing logic did not update the replay protection state accordingly. This allowed an attacker who captured a legitimate frame with pn == 0xFFFFFFFF to replay it indefinitely, as the lowest packet number never advanced and the decryption initialization vector (IV) was reconstructed identically. The fix involved modifying the XPN else-if condition to handle the wrap-around case, ensuring that receipt of pn == U32_MAX properly advances the replay protection state.

References

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