CVE-2026-74660 (GCVE-0-2026-74660)
Vulnerability from cvelistv5
Published
2026-08-22 15:32
Modified
2026-08-25 05:41
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: netfilter: ebt_nflog: pin the NFLOG backend nf_log_unregister() runs after the per-net teardown so its final RCU grace period also drains readers that obtained the logger from a per-net binding. However, ebt_nflog passes an explicit ULOG log type to nf_log_packet() without holding a reference on the selected logger module, unlike the xt_NFLOG and nft_log frontends. An ebtables nflog rule can therefore remain callable while nfnetlink_log is unloaded. The resulting interleaving is: CPU 0 CPU 1 nfnetlink_log_fini() unregister_pernet_subsys() kfree(nfnl_log_pernet(net)) ebt_nflog_tg() nf_log_packet() nfulnl_log_packet() instance_lookup_get_rcu() The global ULOG logger is still registered at this point, so CPU 1 dereferences the per-net state after CPU 0 has freed it. KASAN reported: BUG: KASAN: slab-use-after-free in instance_lookup_get_rcu Read of size 8 at addr ff110001052e6210 by task poc/92 Call Trace: instance_lookup_get_rcu+0x1ce/0x1f0 [nfnetlink_log] nfulnl_log_packet+0x248/0x2fb0 [nfnetlink_log] nf_log_packet+0x204/0x300 ebt_nflog_tg+0x351/0x550 ebt_do_table+0xedf/0x22b0 Allocated by task 90: __kmalloc_noprof+0x186/0x470 ops_init+0x6d/0x420 register_pernet_operations+0x2f6/0x670 register_pernet_subsys+0x23/0x40 Freed by task 93: kfree+0x131/0x3c0 ops_undo_list+0x3e3/0x700 unregister_pernet_operations+0x232/0x490 unregister_pernet_subsys+0x1c/0x30 nfnetlink_log_fini+0x34/0x450 [nfnetlink_log] Acquire the ULOG logger module reference when an ebt_nflog rule is validated and release it when the rule is destroyed. Request the NFLOG backend for legacy callers when needed, matching xt_NFLOG. This prevents module teardown until all ebt_nflog rules have stopped using the logger.
References
Impacted products
Vendor Product Version
Linux Linux Version: c83fa19603bdaeef17b815713dbbe3230c8a34ee
Version: c83fa19603bdaeef17b815713dbbe3230c8a34ee
Version: c83fa19603bdaeef17b815713dbbe3230c8a34ee
Version: c83fa19603bdaeef17b815713dbbe3230c8a34ee
Version: c83fa19603bdaeef17b815713dbbe3230c8a34ee
Version: c83fa19603bdaeef17b815713dbbe3230c8a34ee
Version: c83fa19603bdaeef17b815713dbbe3230c8a34ee
Version: c83fa19603bdaeef17b815713dbbe3230c8a34ee
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/bridge/netfilter/ebt_nflog.c"
          ],
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          "vendor": "Linux",
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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                  "vulnerable": true
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                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: ebt_nflog: pin the NFLOG backend\n\nnf_log_unregister() runs after the per-net teardown so its final RCU\ngrace period also drains readers that obtained the logger from a per-net\nbinding.  However, ebt_nflog passes an explicit ULOG log type to\nnf_log_packet() without holding a reference on the selected logger module,\nunlike the xt_NFLOG and nft_log frontends.\n\nAn ebtables nflog rule can therefore remain callable while nfnetlink_log\nis unloaded.  The resulting interleaving is:\n\n  CPU 0                               CPU 1\n  nfnetlink_log_fini()\n    unregister_pernet_subsys()\n      kfree(nfnl_log_pernet(net))\n                                      ebt_nflog_tg()\n                                        nf_log_packet()\n                                          nfulnl_log_packet()\n                                            instance_lookup_get_rcu()\n\nThe global ULOG logger is still registered at this point, so CPU 1\ndereferences the per-net state after CPU 0 has freed it.  KASAN reported:\n\n  BUG: KASAN: slab-use-after-free in instance_lookup_get_rcu\n  Read of size 8 at addr ff110001052e6210 by task poc/92\n  Call Trace:\n   instance_lookup_get_rcu+0x1ce/0x1f0 [nfnetlink_log]\n   nfulnl_log_packet+0x248/0x2fb0 [nfnetlink_log]\n   nf_log_packet+0x204/0x300\n   ebt_nflog_tg+0x351/0x550\n   ebt_do_table+0xedf/0x22b0\n  Allocated by task 90:\n   __kmalloc_noprof+0x186/0x470\n   ops_init+0x6d/0x420\n   register_pernet_operations+0x2f6/0x670\n   register_pernet_subsys+0x23/0x40\n  Freed by task 93:\n   kfree+0x131/0x3c0\n   ops_undo_list+0x3e3/0x700\n   unregister_pernet_operations+0x232/0x490\n   unregister_pernet_subsys+0x1c/0x30\n   nfnetlink_log_fini+0x34/0x450 [nfnetlink_log]\n\nAcquire the ULOG logger module reference when an ebt_nflog rule is\nvalidated and release it when the rule is destroyed.  Request the NFLOG\nbackend for legacy callers when needed, matching xt_NFLOG.  This prevents\nmodule teardown until all ebt_nflog rules have stopped using the logger."
        }
      ],
      "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"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The UAF is reached through ebtables setsockopt rule installation and nfnetlink_log module teardown (local administrative paths); per kernel CNA guidance, netfilter/ebtables bugs are scored Local even when bridge hook evaluation can be driven by forwarded frames.\nAC:L - The KASAN reproducer uses a deterministic two-thread race between nfnetlink_log_fini() module removal and concurrent bridge traffic through an active ebt_nflog rule; the attacker controls both the unload timing and packet generation without depending on uncontrollable victim state.\nPR:L - Installing an ebt_nflog rule requires CAP_NET_ADMIN in the socket network namespace, obtainable by unprivileged users via user+network namespaces (unshare -Urn); the documented PoC races module teardown concurrently with rule-driven traffic, matching standard CNA treatment for ebtables/netfilter paths.\nUI:N - No victim interaction is required beyond the attacker\u0027s own ebtables configuration, module unload coordination, and bridge traffic generation to hit the active nflog target during the teardown window.\nS:U - The slab use-after-free corrupts host kernel memory within the same security authority; this is not a VM escape, container breakout across an IOMMU boundary, or other cross-scope privilege transition.\nC:H - KASAN confirmed a slab use-after-free read in instance_lookup_get_rcu() against freed nfnl_log_pernet state; UAF on the per-net instance hash table enables attacker-influenced heap reads and disclosure of adjacent kernel memory contents.\nI:H - Use-after-free on the nfnl_log_pernet structure and nfulnl_instance objects provides standard heap grooming primitives; freed slab reuse can redirect subsequent logging operations into attacker-controlled data for arbitrary kernel writes or control-flow hijack.\nA:H - The UAF read on freed per-net logging state can immediately trigger a kernel BUG/oops (as reported by KASAN) and reliably causes denial of service; repeated bridge traffic during module teardown can panic the affected host."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-25T05:41:14.285Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/3bcce49d617c593c7606083bfdb464a1761fa68d"
        },
        {
          "url": "https://git.kernel.org/stable/c/394d7939c6b2b9e6bea0844c89efb5913168d898"
        },
        {
          "url": "https://git.kernel.org/stable/c/2cac4294f184c9bc19ff82552c62b80498694c39"
        },
        {
          "url": "https://git.kernel.org/stable/c/9d8a94b48b393885e7f876c8ef68ed4da5012078"
        },
        {
          "url": "https://git.kernel.org/stable/c/6809379a860b9fccbb5435bf08343f6d081ac68d"
        },
        {
          "url": "https://git.kernel.org/stable/c/47a119ec8a7e2d5c8c4e86fb1a56c4e696e500fb"
        },
        {
          "url": "https://git.kernel.org/stable/c/e2ab7e878bdbe80104c879c31fd2d82a476703b8"
        },
        {
          "url": "https://git.kernel.org/stable/c/30825970339c107bacaf7f61af90fcdb1f597ca1"
        }
      ],
      "title": "netfilter: ebt_nflog: pin the NFLOG backend",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74660",
    "datePublished": "2026-08-22T15:32:33.677Z",
    "dateReserved": "2026-08-15T05:44:03.924Z",
    "dateUpdated": "2026-08-25T05:41:14.285Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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