CVE-2021-47461 (GCVE-0-2021-47461)

Vulnerability from cvelistv5 – Published: 2024-05-22 06:23 – Updated: 2026-08-05 08:47
VLAI
Title
userfaultfd: fix a race between writeprotect and exit_mmap()
Summary
In the Linux kernel, the following vulnerability has been resolved: userfaultfd: fix a race between writeprotect and exit_mmap() A race is possible when a process exits, its VMAs are removed by exit_mmap() and at the same time userfaultfd_writeprotect() is called. The race was detected by KASAN on a development kernel, but it appears to be possible on vanilla kernels as well. Use mmget_not_zero() to prevent the race as done in other userfaultfd operations.
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 2024-05-22 18:15 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 63b2d4174c4ad1f40b48d7138e71bcb564c1fe03 , < 3cda4bfffd4f755645577aaa9e96a606657b4525 (git)
Affected: 63b2d4174c4ad1f40b48d7138e71bcb564c1fe03 , < 149958ecd0627a9f1e9c678c25c665400054cd6a (git)
Affected: 63b2d4174c4ad1f40b48d7138e71bcb564c1fe03 , < cb185d5f1ebf900f4ae3bf84cee212e6dd035aca (git)
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Linux Linux Affected: 5.7
Unaffected: 0 , < 5.7 (semver)
Unaffected: 5.10.76 , ≤ 5.10.* (semver)
Unaffected: 5.14.15 , ≤ 5.14.* (semver)
Unaffected: 5.15 , ≤ * (original_commit_for_fix)
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Show details on NVD website
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                "fs/userfaultfd.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "lessThan": "3cda4bfffd4f755645577aaa9e96a606657b4525",
                  "status": "affected",
                  "version": "63b2d4174c4ad1f40b48d7138e71bcb564c1fe03",
                  "versionType": "git"
                },
                {
                  "lessThan": "149958ecd0627a9f1e9c678c25c665400054cd6a",
                  "status": "affected",
                  "version": "63b2d4174c4ad1f40b48d7138e71bcb564c1fe03",
                  "versionType": "git"
                },
                {
                  "lessThan": "cb185d5f1ebf900f4ae3bf84cee212e6dd035aca",
                  "status": "affected",
                  "version": "63b2d4174c4ad1f40b48d7138e71bcb564c1fe03",
                  "versionType": "git"
                }
              ]
            },
            {
              "defaultStatus": "affected",
              "product": "Linux",
              "programFiles": [
                "fs/userfaultfd.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "status": "affected",
                  "version": "5.7"
                },
                {
                  "lessThan": "5.7",
                  "status": "unaffected",
                  "version": "0",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.10.*",
                  "status": "unaffected",
                  "version": "5.10.76",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.14.*",
                  "status": "unaffected",
                  "version": "5.14.15",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "5.15",
                  "versionType": "original_commit_for_fix"
                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.10.76",
                      "versionStartIncluding": "5.7",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.14.15",
                      "versionStartIncluding": "5.7",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.15",
                      "versionStartIncluding": "5.7",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nuserfaultfd: fix a race between writeprotect and exit_mmap()\n\nA race is possible when a process exits, its VMAs are removed by\nexit_mmap() and at the same time userfaultfd_writeprotect() is called.\n\nThe race was detected by KASAN on a development kernel, but it appears\nto be possible on vanilla kernels as well.\n\nUse mmget_not_zero() to prevent the race as done in other userfaultfd\noperations."
            }
          ],
          "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 bug is reached only via the local userfaultfd(2) syscall and UFFDIO_WRITEPROTECT ioctl into userfaultfd_writeprotect()/mwriteprotect_range(), not via network packet processing or physical device I/O.\nAC:L - The attacker fully controls both sides of the race by creating a userfaultfd, registering a WP range, sharing the fd (fork/SCM_RIGHTS), exiting the mm owner so exit_mmap() frees VMAs, and concurrently issuing UFFDIO_WRITEPROTECT from the fd holder.\nPR:L - Any unprivileged user can open userfaultfd with UFFD_USER_MODE_ONLY (allowed by default) and use UFFDIO_WRITEPROTECT; CAP_SYS_PTRACE is not required for this path.\nUI:N - The attacker performs the uffd setup, fd sharing, process exit, and ioctl hammering themselves; no separate victim action is required.\nS:U - This is a standard in-kernel VMA use-after-free within the host kernel authority, with no VM escape, IOMMU bypass, or other cross-boundary impact.\nC:H - The race is a use-after-free on VMA structures (KASAN-detected) while find_vma/change_protection still touch them; UAF enables reclaim/spray and arbitrary kernel memory disclosure.\nI:H - Use-after-free of VMAs during change_protection allows heap manipulation of VMA state that drives page-table writes, enabling arbitrary write and control-flow hijacking primitives.\nA:H - Concurrent exit_mmap() freeing of VMAs while mwriteprotect_range() walks and modifies them causes kernel oops/panic even when not fully exploited for code execution."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T08:47:57.329Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/3cda4bfffd4f755645577aaa9e96a606657b4525"
            },
            {
              "url": "https://git.kernel.org/stable/c/149958ecd0627a9f1e9c678c25c665400054cd6a"
            },
            {
              "url": "https://git.kernel.org/stable/c/cb185d5f1ebf900f4ae3bf84cee212e6dd035aca"
            }
          ],
          "title": "userfaultfd: fix a race between writeprotect and exit_mmap()",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2021-47461",
        "datePublished": "2024-05-22T06:23:22.373Z",
        "dateReserved": "2024-05-22T06:20:56.197Z",
        "dateUpdated": "2026-08-05T08:47:57.329Z",
        "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

Author Source Type Date Other

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.