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

Vulnerability from cvelistv5 – Published: 2026-08-15 12:27 – Updated: 2026-08-17 05:47
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 , < a28d8903bfe76089ea4bbdbff9976965f9ef8107 (git)
Affected: 23461551c00628c3f3fe9cf837bf53cf8f212b63 , < b14361aca6350ff7907b0e9903c7b94dc7d5d4a0 (git)
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Linux Linux Affected: 3.18
Unaffected: 0 , < 3.18 (semver)
Unaffected: 7.1.8 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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          "product": "Linux",
          "programFiles": [
            "net/ipv4/fou_core.c"
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        }
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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"
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              "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": "2026-08-17T05:47:51.722Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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      "references": [
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          "url": "https://git.kernel.org/stable/c/a28d8903bfe76089ea4bbdbff9976965f9ef8107"
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          "url": "https://git.kernel.org/stable/c/b14361aca6350ff7907b0e9903c7b94dc7d5d4a0"
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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": "2026-08-17T05:47:51.722Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
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      "current_release_date": "2026-08-21T07:57:43+00:00",
      "cve": "CVE-2026-74496",
      "id": "CVE-2026-74496",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:known_affected": "184",
      "product_status:known_not_affected": "90",
      "source": "Red Hat CSAF VEX",
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      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74496.json",
      "version": "3"
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}



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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

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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.