CVE-2026-63925 (GCVE-0-2026-63925)
Vulnerability from cvelistv5
Published
2026-07-19 14:55
Modified
2026-08-05 12:37
Severity ?
8.1 (High) - CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
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).
References
Impacted products
Vendor Product Version
Linux Linux Version: a21ecf0e033807b976967286e6c392f48ee2049f
Version: a21ecf0e033807b976967286e6c392f48ee2049f
Version: a21ecf0e033807b976967286e6c392f48ee2049f
Version: a21ecf0e033807b976967286e6c392f48ee2049f
Version: a21ecf0e033807b976967286e6c392f48ee2049f
Version: a21ecf0e033807b976967286e6c392f48ee2049f
Version: a21ecf0e033807b976967286e6c392f48ee2049f
Version: a21ecf0e033807b976967286e6c392f48ee2049f
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/macsec.c"
          ],
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          "vendor": "Linux",
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          "vendor": "Linux",
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              "status": "unaffected",
              "version": "0",
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              "version": "6.1.176",
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              "version": "6.18.35",
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              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
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                  "vulnerable": true
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                  "versionStartIncluding": "5.7",
                  "vulnerable": true
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                  "versionEndExcluding": "6.6.143",
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                  "versionEndExcluding": "7.1",
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                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmacsec: fix replay protection at XPN lower-PN wrap\n\nIn macsec_post_decrypt(), when pn is U32_MAX, pn + 1 overflows u32 to 0\nand the first branch never fires. If next_pn_halves.lower is also in the\nupper half, pn_same_half(pn, lower) is true and the XPN else-if does not\nfire either, leaving next_pn_halves unchanged. An attacker that captures\nthe legitimate frame carrying pn == 0xFFFFFFFF on an XPN association\ncan then replay it indefinitely, since lowest_pn never rises above\nthe captured pn and macsec_decrypt() reconstructs the same IV.\n\nExtend the XPN else-if to also fire when pn + 1 wraps to 0, so receipt\nof pn == U32_MAX advances next_pn_halves to (upper + 1, 0)."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:A - MACsec processes attacker-supplied Ethernet frames via netdev rx_handler on the underlying link; exploitation requires L2 adjacency on the same broadcast domain or point-to-point MACsec link, not remote Internet reachability.\nAC:L - Once XPN with replay protection is deployed, an on-link attacker can passively capture the single legitimate frame at PN 0xFFFFFFFF and then replay it reliably and indefinitely without races or conditions outside their control.\nPR:N - Exploitation requires only the ability to send or replay Ethernet frames on the MACsec link; no local privileges, capabilities, or authentication on the victim Linux host are needed.\nUI:N - Replay injection is fully attacker-driven after capturing the target frame; no victim user or administrator action is required during exploitation.\nS:U - The flaw bypasses MACsec replay protection within the kernel network stack and does not cross a security boundary such as a VM, container, or IOMMU isolation domain.\nC:N - This is a replay-protection logic flaw, not a memory corruption or decryption weakness; the attacker replays already-captured ciphertext and gains no new confidentiality beyond what passive capture already provided.\nI:H - Bypassing replay protection allows unlimited re-injection of previously authenticated payloads into the controlled port, defeating MACsec\u0027s integrity guarantees and enabling repeated delivery of captured control or data traffic on automotive, industrial, and datacenter MACsec links.\nA:H - The commit confirms captured frames can be replayed indefinitely, enabling sustained injection of decrypted traffic that can overwhelm the receiver and deny service to legitimate peers on the protected link."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:37:20.197Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/dd7306779c6ce1238f4cdc34f3c1f2246b854457"
        },
        {
          "url": "https://git.kernel.org/stable/c/d15130461df388136b62a7b0ce9f66e7e2fa9ff1"
        },
        {
          "url": "https://git.kernel.org/stable/c/23c0e230eab397d7f68be2538790ac41d3bb91fd"
        },
        {
          "url": "https://git.kernel.org/stable/c/679e13a65e68a67c8b3c0467c02ee89157ec6f0f"
        },
        {
          "url": "https://git.kernel.org/stable/c/79495a1b0944fe31ffd54b54b00211b493590d62"
        },
        {
          "url": "https://git.kernel.org/stable/c/6d00f5c7e5ff7ec4795b7f5f8ed88bd346641652"
        },
        {
          "url": "https://git.kernel.org/stable/c/d55acbe577db892b60547b6ef1c020b359331a6d"
        },
        {
          "url": "https://git.kernel.org/stable/c/e68842b3356471ba56c882209f324613dac47f64"
        }
      ],
      "title": "macsec: fix replay protection at XPN lower-PN wrap",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63925",
    "datePublished": "2026-07-19T14:55:26.442Z",
    "dateReserved": "2026-07-19T07:54:57.021Z",
    "dateUpdated": "2026-08-05T12:37:20.197Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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