CVE-2025-21655 (GCVE-0-2025-21655)
Vulnerability from cvelistv5
Published
2025-01-20 13:48
Modified
2026-08-05 11:53
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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
Impacted products
Vendor Product Version
Linux Linux Version: 21a091b970cdbcf3e8ff829234b51be6f9192766
Version: 21a091b970cdbcf3e8ff829234b51be6f9192766
Version: 21a091b970cdbcf3e8ff829234b51be6f9192766
Version: 21a091b970cdbcf3e8ff829234b51be6f9192766
 Create a notification for this product.
Show details on NVD website

To clipboard 

{
  "containers": {
    "adp": [
      {
        "providerMetadata": {
          "dateUpdated": "2025-11-03T20:58:34.729Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
        },
        "references": [
          {
            "url": "https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html"
          }
        ],
        "title": "CVE Program Container"
      },
      {
        "affected": [
          {
            "defaultStatus": "unknown",
            "product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP",
            "vendor": "Siemens",
            "versions": [
              {
                "lessThan": "*",
                "status": "affected",
                "version": "V3.1.6",
                "versionType": "custom"
              }
            ]
          },
          {
            "defaultStatus": "unknown",
            "product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP",
            "vendor": "Siemens",
            "versions": [
              {
                "lessThan": "*",
                "status": "affected",
                "version": "V3.1.6",
                "versionType": "custom"
              }
            ]
          },
          {
            "defaultStatus": "unknown",
            "product": "SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP",
            "vendor": "Siemens",
            "versions": [
              {
                "lessThan": "*",
                "status": "affected",
                "version": "V3.1.6",
                "versionType": "custom"
              }
            ]
          },
          {
            "defaultStatus": "unknown",
            "product": "SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP",
            "vendor": "Siemens",
            "versions": [
              {
                "lessThan": "*",
                "status": "affected",
                "version": "V3.1.6",
                "versionType": "custom"
              }
            ]
          },
          {
            "defaultStatus": "unknown",
            "product": "SIPLUS S7-1500 CPU 1518-4 PN/DP MFP",
            "vendor": "Siemens",
            "versions": [
              {
                "lessThan": "*",
                "status": "affected",
                "version": "V3.1.6",
                "versionType": "custom"
              }
            ]
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-07-14T12:39:38.450Z",
          "orgId": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
          "shortName": "siemens-SADP"
        },
        "references": [
          {
            "url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
          }
        ],
        "x_adpType": "supplier"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "io_uring/eventfd.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "6b63308c28987c6010b1180c72a6db4df6c68033",
              "status": "affected",
              "version": "21a091b970cdbcf3e8ff829234b51be6f9192766",
              "versionType": "git"
            },
            {
              "lessThan": "8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10",
              "status": "affected",
              "version": "21a091b970cdbcf3e8ff829234b51be6f9192766",
              "versionType": "git"
            },
            {
              "lessThan": "a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7",
              "status": "affected",
              "version": "21a091b970cdbcf3e8ff829234b51be6f9192766",
              "versionType": "git"
            },
            {
              "lessThan": "c9a40292a44e78f71258b8522655bffaf5753bdb",
              "status": "affected",
              "version": "21a091b970cdbcf3e8ff829234b51be6f9192766",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "io_uring/eventfd.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.1"
            },
            {
              "lessThan": "6.1",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.125",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.72",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.10",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.13",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.125",
                  "versionStartIncluding": "6.1",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.72",
                  "versionStartIncluding": "6.1",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.10",
                  "versionStartIncluding": "6.1",
                  "vulnerable": true
                },
                {
                  "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": "2026-08-05T11:53:24.723Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.