Vulnerability-Lookup

FKIE_CVE-2025-21655

Vulnerability from fkie_nvd - Published: 2025-01-20 14:15 - Updated: 2026-07-30 06:17

Severity

7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.7 (Medium) - CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Summary

In the Linux kernel, the following vulnerability has been resolved: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period. Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.

References

URL	Tags
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/6b63308c28987c6010b1180c72a6db4df6c68033	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/c9a40292a44e78f71258b8522655bffaf5753bdb	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://project-zero.issues.chromium.org/issues/388499293	Issue Tracking, Third Party Advisory
af854a3a-2127-422b-91ae-364da2661108	https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html
0b142b55-0307-4c5a-b3c9-f314f3fb7c5e	https://cert-portal.siemens.com/productcert/html/ssa-019113.html

Impacted products

Vendor	Product	Version
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	6.13
linux	linux_kernel	6.13
linux	linux_kernel	6.13
linux	linux_kernel	6.13
linux	linux_kernel	6.13
linux	linux_kernel	6.13

JSON

To clipboard

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          "product": "Linux",
          "programFiles": [
            "io_uring/eventfd.c"
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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/eventfd: ensure io_eventfd_signal() defers another RCU period\n\nio_eventfd_do_signal() is invoked from an RCU callback, but when\ndropping the reference to the io_ev_fd, it calls io_eventfd_free()\ndirectly if the refcount drops to zero. This isn\u0027t correct, as any\npotential freeing of the io_ev_fd should be deferred another RCU grace\nperiod.\n\nJust call io_eventfd_put() rather than open-code the dec-and-test and\nfree, which will correctly defer it another RCU grace period."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: io_uring/eventfd: garantizar que io_eventfd_signal() posponga otro per\u00edodo de RCU io_eventfd_do_signal() se invoca desde una devoluci\u00f3n de llamada de RCU, pero al eliminar la referencia a io_ev_fd, llama a io_eventfd_free() directamente si El recuento cae a cero. Esto no es correcto, ya que cualquier posible liberaci\u00f3n de io_ev_fd deber\u00eda posponerse otro per\u00edodo de gracia de RCU. Simplemente llame a io_eventfd_put() en lugar de abrir el c\u00f3digo dec-and-test y free, lo que lo diferir\u00e1 correctamente a otro per\u00edodo de gracia de RCU."
    }
  ],
  "id": "CVE-2025-21655",
  "lastModified": "2026-07-30T06:17:32.767",
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  "vulnStatus": "Modified",
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}

CVE-2025-21655 (GCVE-0-2025-21655)

Vulnerability from cvelistv5 – Published: 2025-01-20 13:48 – Updated: 2026-09-08 08:40

Title

io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period

Summary

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Assigner

Linux mitre root

References

7 references

URL	Tags
https://git.kernel.org/stable/c/6b63308c28987c601…
https://git.kernel.org/stable/c/8efff2aa2d95dc437…
https://git.kernel.org/stable/c/a7085c3ae43b86d4b…
https://git.kernel.org/stable/c/c9a40292a44e78f71…
https://project-zero.issues.chromium.org/issues/3…
https://lists.debian.org/debian-lts-announce/2025…
https://cert-portal.siemens.com/productcert/html/…

Impacted products

5 products

Vendor	Product	Version
Linux	Linux	Affected: 21a091b970cdbcf3e8ff829234b51be6f9192766 , < 6b63308c28987c6010b1180c72a6db4df6c68033 (git) Affected: 21a091b970cdbcf3e8ff829234b51be6f9192766 , < 8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10 (git) Affected: 21a091b970cdbcf3e8ff829234b51be6f9192766 , < a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7 (git) Affected: 21a091b970cdbcf3e8ff829234b51be6f9192766 , < c9a40292a44e78f71258b8522655bffaf5753bdb (git)
Linux	Linux	Affected: 6.1 Unaffected: 0 , < 6.1 (semver) Unaffected: 6.1.125 , ≤ 6.1.* (semver) Unaffected: 6.6.72 , ≤ 6.6.* (semver) Unaffected: 6.12.10 , ≤ 6.12.* (semver) Unaffected: 6.13 , ≤ * (original_commit_for_fix)
Siemens	SIMATIC S7-1500 CPU 1518-4 PN/DP MFP	Affected: V3.1.6 , < * (custom)
Siemens	SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP	Affected: V3.1.6 , < * (custom)
Siemens	SIPLUS S7-1500 CPU 1518-4 PN/DP MFP	Affected: V3.1.6 , < * (custom)

Show details on NVD website

JSON

To clipboard

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          "dateUpdated": "2025-11-03T20:58:34.729Z",
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                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.13",
                  "versionStartIncluding": "6.1",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/eventfd: ensure io_eventfd_signal() defers another RCU period\n\nio_eventfd_do_signal() is invoked from an RCU callback, but when\ndropping the reference to the io_ev_fd, it calls io_eventfd_free()\ndirectly if the refcount drops to zero. This isn\u0027t correct, as any\npotential freeing of the io_ev_fd should be deferred another RCU grace\nperiod.\n\nJust call io_eventfd_put() rather than open-code the dec-and-test and\nfree, which will correctly defer it another RCU grace period."
        }
      ],
      "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 io_uring_setup/io_uring_register/io_uring_enter syscalls and an eventfd write() from a local process. No network-reachable component processes the affected data.\nAC:L - The attacker controls both sides of the race: it deterministically schedules the RCU callback via a write() to a polled eventfd, then issues UNREGISTER_EVENTFD/ring-close during the multi-millisecond grace period while another thread spins in io_eventfd_grab(), and can retry unboundedly by re-registering a fresh ev_fd.\nPR:L - Only an ordinary unprivileged local user account is needed \u2014 sysctl kernel.io_uring_disabled defaults to 0 (io_uring allowed for everyone) and IORING_REGISTER_EVENTFD/IORING_UNREGISTER_EVENTFD perform no capability check.\nUI:N - The attacker performs every step itself \u2014 ring setup, eventfd registration, poll arming, the triggering write(), and the unregister. No victim action is involved.\nS:U - The use-after-free corrupts kernel heap memory within the same security authority; there is no VM, IOMMU, or sandbox boundary crossed.\nC:H - The UAF lets a reallocated kmalloc-64 object supply the -\u003ecq_ev_fd pointer, which is dereferenced as a struct eventfd_ctx *, giving attacker-directed kernel reads and, via typical UAF heap-spray techniques, disclosure of arbitrary kernel memory.\nI:H - The stale object yields an atomic RMW on freed memory, an arbitrary-address increment (ctx-\u003ecount++), a call_rcu() on freed memory, and a wake_up_locked_poll() walking an attacker-controlled waitqueue whose func pointer is invoked \u2014 a control-flow hijack primitive enabling privilege escalation.\nA:H - Freeing io_ev_fd a grace period early reliably produces kernel oops/panic from the UAF read, the atomic RMW on freed memory, and RCU callback-list corruption."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T11:53:24.723Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/6b63308c28987c6010b1180c72a6db4df6c68033"
        },
        {
          "url": "https://git.kernel.org/stable/c/8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10"
        },
        {
          "url": "https://git.kernel.org/stable/c/a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7"
        },
        {
          "url": "https://git.kernel.org/stable/c/c9a40292a44e78f71258b8522655bffaf5753bdb"
        },
        {
          "url": "https://project-zero.issues.chromium.org/issues/388499293"
        }
      ],
      "title": "io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21655",
    "datePublished": "2025-01-20T13:48:40.544Z",
    "dateReserved": "2024-12-29T08:45:45.729Z",
    "dateUpdated": "2026-09-08T08:40:14.559Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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FKIE_CVE-2025-21655

CVE-2025-21655 (GCVE-0-2025-21655)

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