CVE-2021-47123 (GCVE-0-2021-47123)

Vulnerability from cvelistv5 – Published: 2024-03-15 20:14 – Updated: 2026-08-05 08:46
VLAI
Title
io_uring: fix ltout double free on completion race
Summary
In the Linux kernel, the following vulnerability has been resolved: io_uring: fix ltout double free on completion race Always remove linked timeout on io_link_timeout_fn() from the master request link list, otherwise we may get use-after-free when first io_link_timeout_fn() puts linked timeout in the fail path, and then will be found and put on master's free.
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 15:55 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 90cd7e424969d29aff653333b4dcb4e2e199d791 , < 1f64f5e903b9d1d157875721e02adadc9d6f0a5d (git)
Affected: 90cd7e424969d29aff653333b4dcb4e2e199d791 , < 447c19f3b5074409c794b350b10306e1da1ef4ba (git)
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Linux Linux Affected: 5.11
Unaffected: 0 , < 5.11 (semver)
Unaffected: 5.12.10 , ≤ 5.12.* (semver)
Unaffected: 5.13 , ≤ * (original_commit_for_fix)
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                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.12.10",
                      "versionStartIncluding": "5.11",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.13",
                      "versionStartIncluding": "5.11",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring: fix ltout double free on completion race\n\nAlways remove linked timeout on io_link_timeout_fn() from the master\nrequest link list, otherwise we may get use-after-free when first\nio_link_timeout_fn() puts linked timeout in the fail path, and then\nwill be found and put on master\u0027s free."
            }
          ],
          "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 through the local io_uring syscall interface (io_uring_setup/io_uring_enter) by submitting linked SQEs with IORING_OP_LINK_TIMEOUT; it is not reachable from network packet paths.\nAC:L - The race is between linked-timeout hrtimer expiry and master-request completion, both of which the attacker fully controls (timeout duration plus completing the linked op via a pipe/eventfd/etc.), so the race can be driven and retried reliably.\nPR:L - io_uring_setup and IORING_OP_LINK_TIMEOUT require only an unprivileged local account; in the affected 5.11\u20135.12 window there was no io_uring_disabled gate and no capability check beyond optional CAP_IPC_LOCK accounting.\nUI:N - The attacker triggers the race entirely with their own syscalls and does not need any other user to act.\nS:U - Impact is memory corruption inside the host kernel (double-free of an io_kiocb), which is a same-authority privilege-escalation scenario, not a VM/IOMMU/sandbox boundary cross.\nC:H - The bug is a double-free/use-after-free of a slab-allocated io_kiocb; a UAF on that object can be turned into an arbitrary kernel read via heap reuse.\nI:H - Double-free of the linked-timeout request enables heap spraying and write primitives against the freed io_kiocb, supporting control-flow hijacking or arbitrary kernel writes.\nA:H - The same double-free/UAF path reliably produces kernel oopses/panics even without a full exploit, so availability impact is high."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T08:46:07.846Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/1f64f5e903b9d1d157875721e02adadc9d6f0a5d"
            },
            {
              "url": "https://git.kernel.org/stable/c/447c19f3b5074409c794b350b10306e1da1ef4ba"
            }
          ],
          "title": "io_uring: fix ltout double free on completion race",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2021-47123",
        "datePublished": "2024-03-15T20:14:28.888Z",
        "dateReserved": "2024-03-04T18:12:48.839Z",
        "dateUpdated": "2026-08-05T08:46:07.846Z",
        "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.

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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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.