CVE-2025-21851 (GCVE-0-2025-21851)

Vulnerability from cvelistv5 – Published: 2025-03-12 09:42 – Updated: 2026-08-05 11:54
VLAI
Title
bpf: Fix softlockup in arena_map_free on 64k page kernel
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix softlockup in arena_map_free on 64k page kernel On an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y, arena_htab tests cause a segmentation fault and soft lockup. The same failure is not observed with 4k pages on aarch64. It turns out arena_map_free() is calling apply_to_existing_page_range() with the address returned by bpf_arena_get_kern_vm_start(). If this address is not page-aligned the code ends up calling apply_to_pte_range() with that unaligned address causing soft lockup. Fix it by round up GUARD_SZ to PAGE_SIZE << 1 so that the division by 2 in bpf_arena_get_kern_vm_start() returns a page-aligned value.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.3 (Low)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-10-01 19:26 UTC
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 317460317a02a1af512697e6e964298dedd8a163 , < c1f3f3892d4526f18aaeffdb6068ce861e793ee3 (git)
Affected: 317460317a02a1af512697e6e964298dedd8a163 , < 787d556a3de447e70964a4bdeba9196f62a62b1e (git)
Affected: 317460317a02a1af512697e6e964298dedd8a163 , < 517e8a7835e8cfb398a0aeb0133de50e31cae32b (git)
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Linux Linux Affected: 6.9
Unaffected: 0 , < 6.9 (semver)
Unaffected: 6.12.17 , ≤ 6.12.* (semver)
Unaffected: 6.13.5 , ≤ 6.13.* (semver)
Unaffected: 6.14 , ≤ * (original_commit_for_fix)
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                  "attackVector": "LOCAL",
                  "availabilityImpact": "LOW",
                  "baseScore": 3.3,
                  "baseSeverity": "LOW",
                  "confidentialityImpact": "NONE",
                  "integrityImpact": "NONE",
                  "privilegesRequired": "LOW",
                  "scope": "UNCHANGED",
                  "userInteraction": "NONE",
                  "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L",
                  "version": "3.1"
                }
              },
              {
                "other": {
                  "content": {
                    "id": "CVE-2025-21851",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2025-10-01T19:26:12.815420Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "problemTypes": [
              {
                "descriptions": [
                  {
                    "cweId": "CWE-667",
                    "description": "CWE-667 Improper Locking",
                    "lang": "en",
                    "type": "CWE"
                  }
                ]
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2025-10-01T16:58:17.925Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "defaultStatus": "unaffected",
              "product": "Linux",
              "programFiles": [
                "kernel/bpf/arena.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "lessThan": "c1f3f3892d4526f18aaeffdb6068ce861e793ee3",
                  "status": "affected",
                  "version": "317460317a02a1af512697e6e964298dedd8a163",
                  "versionType": "git"
                },
                {
                  "lessThan": "787d556a3de447e70964a4bdeba9196f62a62b1e",
                  "status": "affected",
                  "version": "317460317a02a1af512697e6e964298dedd8a163",
                  "versionType": "git"
                },
                {
                  "lessThan": "517e8a7835e8cfb398a0aeb0133de50e31cae32b",
                  "status": "affected",
                  "version": "317460317a02a1af512697e6e964298dedd8a163",
                  "versionType": "git"
                }
              ]
            },
            {
              "defaultStatus": "affected",
              "product": "Linux",
              "programFiles": [
                "kernel/bpf/arena.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "status": "affected",
                  "version": "6.9"
                },
                {
                  "lessThan": "6.9",
                  "status": "unaffected",
                  "version": "0",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.12.*",
                  "status": "unaffected",
                  "version": "6.12.17",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "6.13.*",
                  "status": "unaffected",
                  "version": "6.13.5",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "6.14",
                  "versionType": "original_commit_for_fix"
                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.12.17",
                      "versionStartIncluding": "6.9",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.13.5",
                      "versionStartIncluding": "6.9",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "6.14",
                      "versionStartIncluding": "6.9",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix softlockup in arena_map_free on 64k page kernel\n\nOn an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y,\narena_htab tests cause a segmentation fault and soft lockup.\nThe same failure is not observed with 4k pages on aarch64.\n\nIt turns out arena_map_free() is calling\napply_to_existing_page_range() with the address returned by\nbpf_arena_get_kern_vm_start().  If this address is not page-aligned\nthe code ends up calling apply_to_pte_range() with that unaligned\naddress causing soft lockup.\n\nFix it by round up GUARD_SZ to PAGE_SIZE \u003c\u003c 1 so that the\ndivision by 2 in bpf_arena_get_kern_vm_start() returns\na page-aligned value."
            }
          ],
          "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 vulnerability is reached through the bpf(2) syscall \u2014 creating a BPF_MAP_TYPE_ARENA map, mmap()ing it, faulting in a page, and closing the fd. No network exposure is involved.\nAC:L - On an affected kernel (arm64 with 64K pages, a mainstream aarch64 distro/server configuration), the unaligned base address makes the non-terminating apply_to_pte_range() loop trigger 100% deterministically with a trivial 4-step sequence; there is no race or memory-layout condition to win.\nPR:L - Arena map creation requires CAP_BPF, but bpf_token_capable() resolves via ns_capable(token-\u003euserns, CAP_BPF), so a delegated BPF token or a container granted CAP_BPF lets an otherwise unprivileged user reach it; this is a delegatable capability, not init-namespace root.\nUI:N - The attacker performs the entire sequence \u2014 map create, mmap, page touch, fd close \u2014 in their own process. No victim action is required.\nS:U - The infinite loop, out-of-bounds page-table walk, and page frees all occur within the kernel\u0027s own security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - Once pte++ walks past the end of the PTE page, arbitrary kernel memory is read and interpreted as page-table entries, and __free_page() on garbage-derived struct pages releases in-use pages for reallocation, which is leverageable for disclosure of other tasks\u0027 data.\nI:H - existing_page_cb() calls __free_page() on struct page pointers decoded from out-of-bounds memory, corrupting page refcounts and prematurely freeing live pages \u2014 a use-after-free primitive suitable for heap grooming and control-flow hijacking.\nA:H - The `while (addr += PAGE_SIZE, addr != end)` loop can never terminate, producing a soft lockup/RCU stall inside a lazy-MMU section on a system workqueue, hanging the machine; the stray page frees compound this into a panic."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T11:54:55.041Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/c1f3f3892d4526f18aaeffdb6068ce861e793ee3"
            },
            {
              "url": "https://git.kernel.org/stable/c/787d556a3de447e70964a4bdeba9196f62a62b1e"
            },
            {
              "url": "https://git.kernel.org/stable/c/517e8a7835e8cfb398a0aeb0133de50e31cae32b"
            }
          ],
          "title": "bpf: Fix softlockup in arena_map_free on 64k page kernel",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2025-21851",
        "datePublished": "2025-03-12T09:42:06.480Z",
        "dateReserved": "2024-12-29T08:45:45.779Z",
        "dateUpdated": "2026-08-05T11:54:55.041Z",
        "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.