CVE-2026-68121 (GCVE-0-2026-68121)

Vulnerability from cvelistv5 – Published: 2026-08-10 11:58 – Updated: 2026-08-13 22:40
VLAI
Title
pppoe: reload header pointer after dev_hard_header()
Summary
In the Linux kernel, the following vulnerability has been resolved: pppoe: reload header pointer after dev_hard_header() pppoe_sendmsg() saves a pointer to the PPPoE header before calling dev_hard_header(). Device header callbacks are allowed to reallocate the skb head, invalidating pointers into it. This can happen when a send is blocked in copy_from_user() while the first non-Ethernet port is added to an empty team device. The team's delegated GRE header callback then expands the skb head. PPPoE subsequently writes six bytes through the stale pointer into the freed head. Reload the PPPoE header through the skb's network-header offset after device header creation. pskb_expand_head() updates that offset when it relocates the head.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < e6493a4d1ee17595766165fa446d45b7e0c318d0 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 7e9fbd7f96bcde63a7c798fe16b38cedee7a1501 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 6866abf59976d273164a6624234d96a967280223 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < bed4caecd723693f750e13adbb2c42ca1249a3fd (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < e9c238f6fe42fb1b4dba3a578277de32cb487937 (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 6.6.148 , ≤ 6.6.* (semver)
Unaffected: 6.12.101 , ≤ 6.12.* (semver)
Unaffected: 6.18.42 , ≤ 6.18.* (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2-rc5 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/ppp/pppoe.c"
          ],
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            "drivers/net/ppp/pppoe.c"
          ],
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          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "2.6.12"
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              "version": "0",
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              "status": "unaffected",
              "version": "6.18.42",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2-rc5",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\npppoe: reload header pointer after dev_hard_header()\n\npppoe_sendmsg() saves a pointer to the PPPoE header before calling\ndev_hard_header(). Device header callbacks are allowed to reallocate the\nskb head, invalidating pointers into it.\n\nThis can happen when a send is blocked in copy_from_user() while the first\nnon-Ethernet port is added to an empty team device. The team\u0027s delegated\nGRE header callback then expands the skb head. PPPoE subsequently writes\nsix bytes through the stale pointer into the freed head.\n\nReload the PPPoE header through the skb\u0027s network-header offset after\ndevice header creation. pskb_expand_head() updates that offset when it\nrelocates the head."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
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            {
              "lang": "en",
              "value": "AV:L - The bug is in pppoe_sendmsg(), reached only via the local sendmsg() syscall on a PF_PPPOX/PPPoE socket; it is not triggered by remote packet reception or in-kernel PPP transmit paths such as __pppoe_xmit().\nAC:L - Exploitation requires a race between copy_from_user() blocking in sendmsg and changing team header_ops (e.g., adding the first non-Ethernet GRE port), which an attacker can drive with concurrent threads and retries rather than uncontrollable timing.\nPR:L - PPPoE sockets can be created without special privileges, and configuring the team/GRE topology needed to trigger dev_hard_header() head expansion is achievable with CAP_NET_ADMIN inside an unprivileged user/network namespace (unshare -Urn).\nUI:N - No victim interaction is required; exploitation is fully attacker-driven through socket I/O and netlink/rtnl configuration of the team device.\nS:U - Impact is kernel heap corruption and privilege escalation within the same kernel security authority, not a cross-boundary escape such as guest-to-host VM breakout or IOMMU bypass.\nC:H - Writing PPPoE header fields through a stale pointer after pskb_expand_head() frees the old skb head is a slab use-after-free; freed kmalloc objects can be reclaimed for sensitive data, enabling arbitrary kernel memory disclosure.\nI:H - The post-dev_hard_header() memcpy/ph-\u003elength stores up to eight attacker-influenced bytes into freed skb head memory, providing a heap corruption primitive that can be developed into arbitrary kernel writes or code execution.\nA:H - Use-after-free writes into freed slab memory commonly cause kernel oops/panic and can be triggered repeatedly via sendmsg, yielding persistent denial of service even when full exploitation is not attempted."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-13T22:40:00.071Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/bed4caecd723693f750e13adbb2c42ca1249a3fd"
        },
        {
          "url": "https://git.kernel.org/stable/c/e9c238f6fe42fb1b4dba3a578277de32cb487937"
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      ],
      "title": "pppoe: reload header pointer after dev_hard_header()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-68121",
    "datePublished": "2026-08-10T11:58:41.489Z",
    "dateReserved": "2026-07-30T09:28:09.369Z",
    "dateUpdated": "2026-08-13T22:40:00.071Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
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      "cve": "CVE-2026-68121",
      "date": "2026-08-13",
      "epss": "0.00175",
      "percentile": "0.07241"
    },
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-08-13T23:09:41+00:00",
      "cve": "CVE-2026-68121",
      "id": "CVE-2026-68121",
      "initial_release_date": "2026-08-10T11:58:41.489000+00:00",
      "product_status:known_affected": "275",
      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel: PPPoE memory corruption via stale pointer",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68121.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.