CVE-2026-63925

Adjacent frame replay via packet-number wraparound

Published Jul 19, 2026 · Updated Jul 19, 2026

Replay-protection bypass in the Linux Kernel MACsec subsystem allows man-in-the-middle attackers to replay an XPN frame indefinitely. The macsec_post_decrypt() path increments a 32-bit packet number at U32_MAX, wraps it to zero, and skips updating next_pn_halves, so macsec_decrypt() reconstructs the same IV. Exploitation requires an XPN association with replay protection and capture of its legitimate 0xFFFFFFFF frame, enabling repeated authenticated-payload delivery and service interruption.

CVSS severity8.1
High
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Replay-protection bypass in the Linux Kernel MACsec subsystem allows man-in-the-middle attackers to replay an XPN frame indefinitely. The macsec_post_decrypt() path increments a 32-bit packet number at U32_MAX, wraps it to zero, and skips updating next_pn_halves, so macsec_decrypt() reconstructs the same IV. Exploitation requires an XPN association with replay protection and capture of its legitimate 0xFFFFFFFF frame, enabling repeated authenticated-payload delivery and service interruption.

The record

CVE
CVE-2026-63925
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-294, T1557
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.7
  2. Affected versionversion=a21ecf0e033807b976967286e6c392f48ee2049f <23c0e230eab397d7f68be2538790ac41d3bb91fd
  3. Affected versionversion=a21ecf0e033807b976967286e6c392f48ee2049f <679e13a65e68a67c8b3c0467c02ee89157ec6f0f
  4. Affected versionversion=a21ecf0e033807b976967286e6c392f48ee2049f <6d00f5c7e5ff7ec4795b7f5f8ed88bd346641652
  5. Affected versionversion=a21ecf0e033807b976967286e6c392f48ee2049f <79495a1b0944fe31ffd54b54b00211b493590d62
  6. Affected versionversion=a21ecf0e033807b976967286e6c392f48ee2049f <d15130461df388136b62a7b0ce9f66e7e2fa9ff1
  7. Affected versionversion=a21ecf0e033807b976967286e6c392f48ee2049f <d55acbe577db892b60547b6ef1c020b359331a6d
  8. Affected versionversion=a21ecf0e033807b976967286e6c392f48ee2049f <dd7306779c6ce1238f4cdc34f3c1f2246b854457
  9. Affected versionversion=a21ecf0e033807b976967286e6c392f48ee2049f <e68842b3356471ba56c882209f324613dac47f64

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=5.7; version=a21ecf0e033807b976967286e6c392f48ee2049f <23c0e230eab397d7f68be2538790ac41d3bb91fd; version=a21ecf0e033807b976967286e6c392f48ee2049f <679e13a65e68a67c8b3c0467c02ee89157ec6f0f; version=a21ecf0e033807b976967286e6c392f48ee2049f <6d00f5c7e5ff7ec4795b7f5f8ed88bd346641652; version=a21ecf0e033807b976967286e6c392f48ee2049f <79495a1b0944fe31ffd54b54b00211b493590d62; version=a21ecf0e033807b976967286e6c392f48ee2049f <d15130461df388136b62a7b0ce9f66e7e2fa9ff1; version=a21ecf0e033807b976967286e6c392f48ee2049f <d55acbe577db892b60547b6ef1c020b359331a6d; version=a21ecf0e033807b976967286e6c392f48ee2049f <dd7306779c6ce1238f4cdc34f3c1f2246b854457; version=a21ecf0e033807b976967286e6c392f48ee2049f <e68842b3356471ba56c882209f324613dac47f64

Published CVSS scores

8.1Linux CNACVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-294Authentication Bypass by Capture-replay
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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