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CVE-2021-47014 (GCVE-0-2021-47014)

Vulnerability from cvelistv5 – Published: 2024-02-28 08:13 – Updated: 2026-08-05 08:45
VLAI
Title
net/sched: act_ct: fix wild memory access when clearing fragments
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: act_ct: fix wild memory access when clearing fragments while testing re-assembly/re-fragmentation using act_ct, it's possible to observe a crash like the following one: KASAN: maybe wild-memory-access in range [0x0001000000000448-0x000100000000044f] CPU: 50 PID: 0 Comm: swapper/50 Tainted: G S 5.12.0-rc7+ #424 Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017 RIP: 0010:inet_frag_rbtree_purge+0x50/0xc0 Code: 00 fc ff df 48 89 c3 31 ed 48 89 df e8 a9 7a 38 ff 4c 89 fe 48 89 df 49 89 c6 e8 5b 3a 38 ff 48 8d 7b 40 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 75 59 48 8d bb d0 00 00 00 4c 8b 6b 40 48 89 f8 48 RSP: 0018:ffff888c31449db8 EFLAGS: 00010203 RAX: 0000200000000089 RBX: 000100000000040e RCX: ffffffff989eb960 RDX: 0000000000000140 RSI: ffffffff97cfb977 RDI: 000100000000044e RBP: 0000000000000900 R08: 0000000000000000 R09: ffffed1186289350 R10: 0000000000000003 R11: ffffed1186289350 R12: dffffc0000000000 R13: 000100000000040e R14: 0000000000000000 R15: ffff888155e02160 FS: 0000000000000000(0000) GS:ffff888c31440000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00005600cb70a5b8 CR3: 0000000a2c014005 CR4: 00000000003706e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <IRQ> inet_frag_destroy+0xa9/0x150 call_timer_fn+0x2d/0x180 run_timer_softirq+0x4fe/0xe70 __do_softirq+0x197/0x5a0 irq_exit_rcu+0x1de/0x200 sysvec_apic_timer_interrupt+0x6b/0x80 </IRQ> when act_ct temporarily stores an IP fragment, restoring the skb qdisc cb results in putting random data in FRAG_CB(), and this causes those "wild" memory accesses later, when the rbtree is purged. Never overwrite the skb cb in case tcf_ct_handle_fragments() returns -EINPROGRESS.
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 2024-09-10 15:58 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: ae372cb1750f6c95370f92fe5f5620e0954663ba , < 0648941f4c8bbf8b4b6c0b270889ae7aa769b921 (git)
Affected: ae372cb1750f6c95370f92fe5f5620e0954663ba , < f77bd544a6bbe69aa50d9ed09f13494cf36ff806 (git)
Affected: fbff97eb6f4a94a3f15f685bed604c9adc29ac3e (git)
Affected: 5.7.12 , < 5.8 (semver)
guessed Create a notification for this product.
Linux Linux Affected: 5.8
Unaffected: 0 , < 5.8 (semver)
Unaffected: 5.12.4 , ≤ 5.12.* (semver)
Unaffected: 5.13 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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          },
          {
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            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/0648941f4c8bbf8b4b6c0b270889ae7aa769b921"
          },
          {
            "source": "af854a3a-2127-422b-91ae-364da2661108",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/f77bd544a6bbe69aa50d9ed09f13494cf36ff806"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Modified",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-754"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-08-04T23:06:11+00:00",
      "cve": "CVE-2021-47014",
      "id": "CVE-2021-47014",
      "initial_release_date": "2021-01-01T00:00:00+00:00",
      "product_status:known_affected": "198",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net/sched: act_ct: fix wild memory access when clearing fragments",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-47014.json",
      "version": "3"
    },
    "vulnrichment": {
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            "providerMetadata": {
              "dateUpdated": "2024-08-04T05:24:38.521Z",
              "orgId": "af854a3a-2127-422b-91ae-364da2661108",
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                "url": "https://git.kernel.org/stable/c/f77bd544a6bbe69aa50d9ed09f13494cf36ff806"
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            ],
            "title": "CVE Program Container"
          },
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2021-47014",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2024-09-10T15:58:12.683000Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
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            "providerMetadata": {
              "dateUpdated": "2024-09-11T12:42:17.112Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
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        ],
        "cna": {
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              "defaultStatus": "unaffected",
              "product": "Linux",
              "programFiles": [
                "net/sched/act_ct.c"
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
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                  "status": "affected",
                  "version": "5.7.12",
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              "versions": [
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                  "version": "5.12.4",
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                  "status": "unaffected",
                  "version": "5.13",
                  "versionType": "original_commit_for_fix"
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                      "versionStartIncluding": "5.8",
                      "vulnerable": true
                    },
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                      "versionEndExcluding": "5.13",
                      "versionStartIncluding": "5.8",
                      "vulnerable": true
                    },
                    {
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                      "vulnerable": true
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                  ],
                  "negate": false,
                  "operator": "OR"
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            }
          ],
          "descriptions": [
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              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_ct: fix wild memory access when clearing fragments\n\nwhile testing re-assembly/re-fragmentation using act_ct, it\u0027s possible to\nobserve a crash like the following one:\n\n KASAN: maybe wild-memory-access in range [0x0001000000000448-0x000100000000044f]\n CPU: 50 PID: 0 Comm: swapper/50 Tainted: G S                5.12.0-rc7+ #424\n Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017\n RIP: 0010:inet_frag_rbtree_purge+0x50/0xc0\n Code: 00 fc ff df 48 89 c3 31 ed 48 89 df e8 a9 7a 38 ff 4c 89 fe 48 89 df 49 89 c6 e8 5b 3a 38 ff 48 8d 7b 40 48 89 f8 48 c1 e8 03 \u003c42\u003e 80 3c 20 00 75 59 48 8d bb d0 00 00 00 4c 8b 6b 40 48 89 f8 48\n RSP: 0018:ffff888c31449db8 EFLAGS: 00010203\n RAX: 0000200000000089 RBX: 000100000000040e RCX: ffffffff989eb960\n RDX: 0000000000000140 RSI: ffffffff97cfb977 RDI: 000100000000044e\n RBP: 0000000000000900 R08: 0000000000000000 R09: ffffed1186289350\n R10: 0000000000000003 R11: ffffed1186289350 R12: dffffc0000000000\n R13: 000100000000040e R14: 0000000000000000 R15: ffff888155e02160\n FS:  0000000000000000(0000) GS:ffff888c31440000(0000) knlGS:0000000000000000\n CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: 00005600cb70a5b8 CR3: 0000000a2c014005 CR4: 00000000003706e0\n DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\n DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\n Call Trace:\n  \u003cIRQ\u003e\n  inet_frag_destroy+0xa9/0x150\n  call_timer_fn+0x2d/0x180\n  run_timer_softirq+0x4fe/0xe70\n  __do_softirq+0x197/0x5a0\n  irq_exit_rcu+0x1de/0x200\n  sysvec_apic_timer_interrupt+0x6b/0x80\n  \u003c/IRQ\u003e\n\nwhen act_ct temporarily stores an IP fragment, restoring the skb qdisc cb\nresults in putting random data in FRAG_CB(), and this causes those \"wild\"\nmemory accesses later, when the rbtree is purged. Never overwrite the skb\ncb in case tcf_ct_handle_fragments() returns -EINPROGRESS."
            }
          ],
          "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"
              },
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                {
                  "lang": "en",
                  "value": "AV:L - The bug is in the tc act_ct datapath and is reached after installing flower/act_ct via local netlink; per kernel CNA guidance, tc/qdisc bugs are Local even when later driven by packets.\nAC:L - An attacker who installs act_ct and sends incomplete IP fragments reliably corrupts FRAG_CB and later triggers inet_frag_rbtree_purge; no race or layout outside attacker control is required.\nPR:L - Installing nested act_ct via tc filters requires CAP_NET_ADMIN checked against the netns user_ns (cls_api netlink_ns_capable), which an unprivileged user obtains with unshare -Urn.\nUI:N - The attacker configures act_ct and injects fragments themselves; no separate victim action is required.\nS:U - Impact is confined to host kernel memory within the same security authority; there is no VM, IOMMU, or sandbox boundary cross.\nC:H - Restoring qdisc_skb_cb over FRAG_CB corrupts next_frag, and purge later dereferences that wild pointer while walking/freeing skbs, which is memory corruption leverageable for kernel disclosure.\nI:H - The corrupted next_frag linked-list walk ends in kfree_skb on attacker-influenced pointers, yielding a heap corruption/arbitrary-free primitive exploitable for control-flow hijack.\nA:H - The bug demonstrably causes KASAN wild-memory-access and kernel oops in inet_frag_rbtree_purge from softirq, which is a complete availability impact."
                }
              ]
            }
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          "providerMetadata": {
            "dateUpdated": "2026-08-05T08:45:35.578Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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              "url": "https://git.kernel.org/stable/c/f77bd544a6bbe69aa50d9ed09f13494cf36ff806"
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          "title": "net/sched: act_ct: fix wild memory access when clearing fragments",
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            "engine": "bippy-1.2.0"
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      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2021-47014",
        "datePublished": "2024-02-28T08:13:31.513Z",
        "dateReserved": "2024-02-27T18:42:55.953Z",
        "dateUpdated": "2026-08-05T08:45:35.578Z",
        "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.

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.


Related by attack behaviour

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.