CVE-2026-74496 (GCVE-0-2026-74496)

Vulnerability from cvelistv5 – Published: 2026-08-15 12:27 – Updated: 2026-09-21 13:14
VLAI
Title
fou: Fix use-after-free in fou_create()
Summary
In the Linux kernel, the following vulnerability has been resolved: fou: Fix use-after-free in fou_create() fou_create() publishes struct fou through sk_user_data before adding the new FOU port to the per-netns list. If fou_add_to_port_list() fails, the error path frees fou while it is still reachable through sk_user_data. A concurrent receive can then dereference the freed object in fou_from_sock(). This ordering issue was previously noted in the linked discussion. The failure is reachable when local port 0 is requested. Each socket binds to a different ephemeral port, but fou_cfg_cmp() compares the requested port 0 and reports -EALREADY once an entry already exists. Release the tunnel socket before freeing fou so sk_user_data is cleared first, and defer reclamation with kfree_rcu() to protect concurrent RCU readers. This matches the lifetime handling in fou_release().
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 CPE status
Linux Linux Affected: 23461551c00628c3f3fe9cf837bf53cf8f212b63 , < 58835985c035a8333742f829ad7e0889a082f9d3 (git)
Affected: 23461551c00628c3f3fe9cf837bf53cf8f212b63 , < 9042867d4701728f0c6527215b11471759904d8f (git)
Affected: 23461551c00628c3f3fe9cf837bf53cf8f212b63 , < a28d8903bfe76089ea4bbdbff9976965f9ef8107 (git)
Affected: 23461551c00628c3f3fe9cf837bf53cf8f212b63 , < b14361aca6350ff7907b0e9903c7b94dc7d5d4a0 (git)
guessed Create a notification for this product.
Linux Linux Affected: 3.18
Unaffected: 0 , < 3.18 (semver)
Unaffected: 6.12.111 , ≤ 6.12.* (semver)
Unaffected: 6.18.53 , ≤ 6.18.* (semver)
Unaffected: 7.1.8 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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          "product": "Linux",
          "programFiles": [
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              "versionType": "semver"
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                  "versionStartIncluding": "3.18",
                  "vulnerable": true
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                {
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                  "versionEndExcluding": "6.18.53",
                  "versionStartIncluding": "3.18",
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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\nfou: Fix use-after-free in fou_create()\n\nfou_create() publishes struct fou through sk_user_data before adding the\nnew FOU port to the per-netns list.  If fou_add_to_port_list() fails,\nthe error path frees fou while it is still reachable through\nsk_user_data.  A concurrent receive can then dereference the freed\nobject in fou_from_sock().\n\nThis ordering issue was previously noted in the linked discussion.\n\nThe failure is reachable when local port 0 is requested.  Each socket\nbinds to a different ephemeral port, but fou_cfg_cmp() compares the\nrequested port 0 and reports -EALREADY once an entry already exists.\n\nRelease the tunnel socket before freeing fou so sk_user_data is cleared\nfirst, and defer reclamation with kfree_rcu() to protect concurrent RCU\nreaders.  This matches the lifetime handling in fou_release()."
        }
      ],
      "metrics": [
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            "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"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The UAF is opened only via local FOU_CMD_ADD genetlink into fou_create(); remote UDP can race the dangling sk_user_data read in fou_udp_recv/gue_udp_recv but cannot alone reach the erroneous teardown path.\nAC:L - An attacker with CAP_NET_ADMIN controls both sides: issue a second FOU_CMD_ADD with port 0 to force -EALREADY on fou_add_to_port_list while concurrently sending UDP/GRO traffic to the just-bound ephemeral socket during the kfree window.\nPR:L - FOU_CMD_ADD is gated by GENL_ADMIN_PERM (CAP_NET_ADMIN); the fou genl family is netnsok, so a user with CAP_NET_ADMIN inside unshare -Urn can configure FOU and trigger the failing add path without init-namespace root.\nUI:N - Exploitation is fully programmatic via concurrent netlink FOU_CMD_ADD requests and attacker-controlled UDP packets; no victim mount, file open, or other interactive action is required.\nS:U - Impact is kernel heap corruption and privilege escalation within the same security authority; this is not a VM escape, IOMMU bypass, or other cross-boundary scope change.\nC:H - Concurrent readers call fou_from_sock() and dereference freed struct fou fields (family, protocol, flags); reclaimed slab contents give attacker-controlled reads and kernel pointer disclosure primitives typical of UAF.\nI:H - Freed struct fou is attacker-reclaimable kmalloc memory; fou_gro_receive indexes inet_offloads[fou-\u003eprotocol] from the dangling pointer, enabling heap grooming for arbitrary writes and control-flow hijack.\nA:H - Use-after-free in UDP receive/GRO softirq reliably causes KASAN violations and, on production kernels, invalid pointer dereferences or panics when accessing the freed fou object during packet processing."
            }
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        "dateUpdated": "2026-09-21T13:14:05.619Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74496",
    "datePublished": "2026-08-15T12:27:23.854Z",
    "dateReserved": "2026-08-15T05:44:03.906Z",
    "dateUpdated": "2026-09-21T13:14:05.619Z",
    "state": "PUBLISHED"
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      "version": "1"
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          }
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        "lastModified": "2026-09-21T14:17:19.223",
        "metrics": {
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                "confidentialityImpact": "HIGH",
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      "cve": "CVE-2026-74496",
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      "title": "kernel: fou: Fix use-after-free in fou_create()",
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      "cve": "CVE-2026-74496",
      "id": "CVE-2026-74496",
      "initial_release_date": "2026-08-21T00:40:43Z",
      "product_status:first_fixed": "127",
      "product_status:known_affected": "701",
      "product_status:known_not_affected": "4",
      "product_status:recommended": "107",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-74496",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74496.json",
      "version": "10"
    }
  }
}



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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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  • 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.


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