CVE-2026-97938 (GCVE-0-2026-97938)

Vulnerability from cvelistv5 – Published: 2026-09-25 10:22 – Updated: 2026-09-25 10:22
VLAI
Title
reboot: fix cad_pid use-after-free race
Summary
In the Linux kernel, the following vulnerability has been resolved: reboot: fix cad_pid use-after-free race cad_pid is a single kernel-wide struct pid pointer. proc_do_cad_pid() reads it and passes it to pid_vnr() without protecting the lifetime of the referenced struct pid. A concurrent writer can replace cad_pid and drop the final reference to the old struct pid after the reader has loaded the pointer but before pid_vnr() has finished dereferencing it, causing a use-after-free. kill_cad_pid() has the same lifetime race when it passes cad_pid to kill_pid(). At the time this issue was reported, an unprivileged user could reach the sysctl through user and PID namespaces because cad_pid was registered in pid_table[]. Moving cad_pid back to the global reboot sysctl table corrected that namespace and permission mismatch, but did not fix the underlying lifetime race. Fix this by treating cad_pid as an RCU-protected pointer at both read sites and by waiting for a grace period before dropping the old reference on the write side. call_rcu(&old_pid->rcu, ...) cannot be used here because free_pid() also queues pid->rcu; queueing the same rcu_head twice can corrupt the RCU callback list. Original KASAN crash stack: kernel/pid.c:545 pid_nr_ns() # reads freed pid->level kernel/pid.c:556 pid_vnr() # calls pid_nr_ns() kernel/pid.c:775 proc_do_cad_pid() # calls pid_vnr(cad_pid)
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 9ec52099e4b8678a60e9f93e41ad87885d64f3e6 , < ad72e2566643fff7f01666d845fb026898155e1f (git)
Affected: 9ec52099e4b8678a60e9f93e41ad87885d64f3e6 , < 9a17b0e053197a6a42cdc75e75a35b17aa662088 (git)
Affected: 9ec52099e4b8678a60e9f93e41ad87885d64f3e6 , < 5a88f78df753993469dab4d1831f8fb4256a9468 (git)
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Linux Linux Affected: 2.6.19
Unaffected: 0 , < 2.6.19 (semver)
Unaffected: 6.18.53 , ≤ 6.18.* (semver)
Unaffected: 7.2.7 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc3 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
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          "product": "Linux",
          "programFiles": [
            "include/linux/sched.h",
            "include/linux/sched/signal.h",
            "init/main.c",
            "kernel/reboot.c",
            "kernel/signal.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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          "vendor": "Linux",
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              "versionType": "original_commit_for_fix"
            }
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      "cpeApplicability": [
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          "nodes": [
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                  "vulnerable": true
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                  "vulnerable": true
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                  "vulnerable": true
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              "negate": false,
              "operator": "OR"
            }
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        }
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nreboot: fix cad_pid use-after-free race\n\ncad_pid is a single kernel-wide struct pid pointer. proc_do_cad_pid()\nreads it and passes it to pid_vnr() without protecting the lifetime of\nthe referenced struct pid. A concurrent writer can replace cad_pid and\ndrop the final reference to the old struct pid after the reader has\nloaded the pointer but before pid_vnr() has finished dereferencing it,\ncausing a use-after-free.\n\nkill_cad_pid() has the same lifetime race when it passes cad_pid to\nkill_pid().\n\nAt the time this issue was reported, an unprivileged user could reach the\nsysctl through user and PID namespaces because cad_pid was registered in\npid_table[]. Moving cad_pid back to the global reboot sysctl table\ncorrected that namespace and permission mismatch, but did not fix the\nunderlying lifetime race.\n\nFix this by treating cad_pid as an RCU-protected pointer at both read\nsites and by waiting for a grace period before dropping the old reference\non the write side.\n\ncall_rcu(\u0026old_pid-\u003ercu, ...) cannot be used here because free_pid()\nalso queues pid-\u003ercu; queueing the same rcu_head twice can corrupt the\nRCU callback list.\n\nOriginal KASAN crash stack:\n  kernel/pid.c:545 pid_nr_ns()        # reads freed pid-\u003elevel\n  kernel/pid.c:556 pid_vnr()          # calls pid_nr_ns()\n  kernel/pid.c:775 proc_do_cad_pid()  # calls pid_vnr(cad_pid)"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-25T10:22:51.720Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/ad72e2566643fff7f01666d845fb026898155e1f"
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        {
          "url": "https://git.kernel.org/stable/c/9a17b0e053197a6a42cdc75e75a35b17aa662088"
        },
        {
          "url": "https://git.kernel.org/stable/c/5a88f78df753993469dab4d1831f8fb4256a9468"
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      ],
      "title": "reboot: fix cad_pid use-after-free race",
      "x_generator": {
        "engine": "bippy-1.2.0"
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    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-97938",
    "datePublished": "2026-09-25T10:22:51.720Z",
    "dateReserved": "2026-09-25T10:18:58.204Z",
    "dateUpdated": "2026-09-25T10:22:51.720Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-97938",
      "date": "2026-09-27",
      "epss": "0.00198",
      "percentile": "0.08592"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-27T23:53:38.000Z",
      "cve": "CVE-2026-97938",
      "id": "msrc_CVE-2026-97938",
      "initial_release_date": "2026-09-27T23:53:38.000Z",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "reboot: fix cad_pid use-after-free race",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-97938.json",
      "version": "1"
    },
    "nvd": {
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                  "include/linux/sched/signal.h",
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                  "kernel/reboot.c",
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                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "status": "affected",
                    "version": "2.6.19"
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                    "version": "0",
                    "versionType": "semver"
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                    "status": "unaffected",
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                    "versionType": "semver"
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                    "status": "unaffected",
                    "version": "7.2.7",
                    "versionType": "semver"
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                    "version": "7.3-rc3",
                    "versionType": "original_commit_for_fix"
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              }
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nreboot: fix cad_pid use-after-free race\n\ncad_pid is a single kernel-wide struct pid pointer. proc_do_cad_pid()\nreads it and passes it to pid_vnr() without protecting the lifetime of\nthe referenced struct pid. A concurrent writer can replace cad_pid and\ndrop the final reference to the old struct pid after the reader has\nloaded the pointer but before pid_vnr() has finished dereferencing it,\ncausing a use-after-free.\n\nkill_cad_pid() has the same lifetime race when it passes cad_pid to\nkill_pid().\n\nAt the time this issue was reported, an unprivileged user could reach the\nsysctl through user and PID namespaces because cad_pid was registered in\npid_table[]. Moving cad_pid back to the global reboot sysctl table\ncorrected that namespace and permission mismatch, but did not fix the\nunderlying lifetime race.\n\nFix this by treating cad_pid as an RCU-protected pointer at both read\nsites and by waiting for a grace period before dropping the old reference\non the write side.\n\ncall_rcu(\u0026old_pid-\u003ercu, ...) cannot be used here because free_pid()\nalso queues pid-\u003ercu; queueing the same rcu_head twice can corrupt the\nRCU callback list.\n\nOriginal KASAN crash stack:\n  kernel/pid.c:545 pid_nr_ns()        # reads freed pid-\u003elevel\n  kernel/pid.c:556 pid_vnr()          # calls pid_nr_ns()\n  kernel/pid.c:775 proc_do_cad_pid()  # calls pid_vnr(cad_pid)"
          }
        ],
        "id": "CVE-2026-97938",
        "lastModified": "2026-09-25T11:17:21.193",
        "metrics": {},
        "published": "2026-09-25T11:17:21.193",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/5a88f78df753993469dab4d1831f8fb4256a9468"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/ad72e2566643fff7f01666d845fb026898155e1f"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    }
  }
}



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