CVE-2021-47394 (GCVE-0-2021-47394)

Vulnerability from cvelistv5 – Published: 2024-05-21 15:03 – Updated: 2026-08-05 08:47
VLAI
Title
netfilter: nf_tables: unlink table before deleting it
Summary
In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: unlink table before deleting it syzbot reports following UAF: BUG: KASAN: use-after-free in memcmp+0x18f/0x1c0 lib/string.c:955 nla_strcmp+0xf2/0x130 lib/nlattr.c:836 nft_table_lookup.part.0+0x1a2/0x460 net/netfilter/nf_tables_api.c:570 nft_table_lookup net/netfilter/nf_tables_api.c:4064 [inline] nf_tables_getset+0x1b3/0x860 net/netfilter/nf_tables_api.c:4064 nfnetlink_rcv_msg+0x659/0x13f0 net/netfilter/nfnetlink.c:285 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504 Problem is that all get operations are lockless, so the commit_mutex held by nft_rcv_nl_event() isn't enough to stop a parallel GET request from doing read-accesses to the table object even after synchronize_rcu(). To avoid this, unlink the table first and store the table objects in on-stack scratch space.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-05-28 18:27 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 6001a930ce0378b62210d4f83583fc88a903d89d , < f65c73d3aabb87d4353e0bc4a718b5ae8c43fd04 (git)
Affected: 6001a930ce0378b62210d4f83583fc88a903d89d , < a499b03bf36b0c2e3b958a381d828678ab0ffc5e (git)
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Linux Linux Affected: 5.12
Unaffected: 0 , < 5.12 (semver)
Unaffected: 5.14.10 , ≤ 5.14.* (semver)
Unaffected: 5.15 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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            "source": "nvd@nist.gov",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-13T19:34:56+00:00",
      "cve": "CVE-2021-47394",
      "id": "CVE-2021-47394",
      "initial_release_date": "2021-01-01T00:00:00+00:00",
      "product_status:known_affected": "28",
      "product_status:known_not_affected": "170",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: netfilter: nf_tables: unlink table before deleting it",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-47394.json",
      "version": "3"
    },
    "suse_vex": {
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      "current_release_date": "2026-09-03T00:45:23Z",
      "cve": "CVE-2021-47394",
      "id": "CVE-2021-47394",
      "initial_release_date": "2024-05-28T03:34:19Z",
      "product_status:known_affected": "275",
      "product_status:known_not_affected": "266",
      "product_status:recommended": "452",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2021-47394",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-47394.json",
      "version": "53"
    },
    "vulnrichment": {
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            ],
            "title": "CVE Program Container"
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          {
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                  "content": {
                    "id": "CVE-2021-47394",
                    "options": [
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                      },
                      {
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                      },
                      {
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                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2024-05-28T18:27:57.258962Z",
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            "title": "CISA ADP Vulnrichment"
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              "vendor": "Linux",
              "versions": [
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                {
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                  "version": "0",
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              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nf_tables: unlink table before deleting it\n\nsyzbot reports following UAF:\nBUG: KASAN: use-after-free in memcmp+0x18f/0x1c0 lib/string.c:955\n nla_strcmp+0xf2/0x130 lib/nlattr.c:836\n nft_table_lookup.part.0+0x1a2/0x460 net/netfilter/nf_tables_api.c:570\n nft_table_lookup net/netfilter/nf_tables_api.c:4064 [inline]\n nf_tables_getset+0x1b3/0x860 net/netfilter/nf_tables_api.c:4064\n nfnetlink_rcv_msg+0x659/0x13f0 net/netfilter/nfnetlink.c:285\n netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504\n\nProblem is that all get operations are lockless, so the commit_mutex\nheld by nft_rcv_nl_event() isn\u0027t enough to stop a parallel GET request\nfrom doing read-accesses to the table object even after synchronize_rcu().\n\nTo avoid this, unlink the table first and store the table objects in\non-stack scratch space."
            }
          ],
          "metrics": [
            {
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                "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 bug is reached only through the local nfnetlink/nftables control plane (NETLINK_NETFILTER create of an owned table, lockless GET*, and socket close triggering NETLINK_URELEASE\u2192nft_rcv_nl_event), not via remote packet processing.\nAC:L - The attacker controls both sides of the race\u2014creating an NFT_TABLE_F_OWNER table, spamming parallel RCU GET lookups from another netlink socket, and closing the owner socket\u2014so the post-synchronize_rcu free-while-still-linked window is reliably hittable.\nPR:L - nfnetlink_rcv() requires CAP_NET_ADMIN via netlink_net_capable() against the network namespace\u2019s user_ns, which an unprivileged user obtains with unshare -Urn; nftables is fully usable per-netns.\nUI:N - Exploitation needs no victim action; the attacker creates the owned table, drives concurrent GET requests, and closes their own netlink socket to trigger the UAF.\nS:U - Impact is confined to the local kernel privilege boundary (heap UAF / local privilege escalation) with no VM, IOMMU, or cross-authority escape.\nC:H - The race frees the still-linked nft_table (and its name/contents) while lockless nft_table_lookup reads it via nla_strcmp; this classic UAF enables heap spray and arbitrary kernel read primitives.\nI:H - __nft_release_table destroys the table and nested objects while concurrent GET paths can still observe and follow those pointers, yielding reclaimable UAF/write primitives suitable for control-flow hijacking.\nA:H - Use-after-free of the table during GET lookup causes kernel oops/panic (as shown by the KASAN report in memcmp/nla_strcmp), and the attacker can trigger it repeatedly."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T08:47:37.812Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
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            {
              "url": "https://git.kernel.org/stable/c/a499b03bf36b0c2e3b958a381d828678ab0ffc5e"
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          "title": "netfilter: nf_tables: unlink table before deleting it",
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      "cveMetadata": {
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        "assignerShortName": "Linux",
        "cveId": "CVE-2021-47394",
        "datePublished": "2024-05-21T15:03:51.503Z",
        "dateReserved": "2024-05-21T14:58:30.814Z",
        "dateUpdated": "2026-08-05T08:47:37.812Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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.

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  • 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.
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  • 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.



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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.