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CVE-2026-64560

Estado: RecibidaAlta (7.8)—

In the Linux kernel, the following vulnerability has been resolved:

posix-cpu-timers: Prevent UAF caused by non-leader exec() race

Wongi and Jungwoo decoded and reported a non-leader exec() related race which can result in an UAF:

This is "harmless" unless the deleted timer was armed and enqueued in p->signal because on exec() a TGID targeted timer is inherited.

As sys_timer_delete() freed the underlying posix timer object run_posix_cpu_timers() or any timerqueue related add/delete operations on other timers will access the freed object's timerqueue node, which results in an UAF.

There is a similar problem vs. posix_cpu_timer_set(). For regular posix timers it just transiently returns -ESRCH to user space, but for the use case in do_cpu_nanosleep() it's the same UAF just that the k_itimer is allocated on the stack.

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Also posix_cpu_timer_rearm() fails to rearm the timer, which means it stops to expire.

While debating solutions Frederic pointed out another problem:

On weakly ordered architectures it is not guaranteed that posix_cpu_timer_del() will observe the stores in posix_cpu_timers*_exit() when p->sighand is observed as NULL, which means the WARN() can be a false positive.

Solve these issues by:

#1/#2 ensures that the reader side which observes sighand == NULL also observes all preceeding stores, i.e. the stores in posix_cpu_timers*_exit() and the ones in unhash_task().

#3 ensures that the above described non-leader exec() situation is handled gracefully. When the task lookup returns the old leader, but sighand == NULL then it retries. In the non-leader exec() case the subsequent task lookup will observe the new leader due to #1/#2. In normal exit() scenarios the subsequent lookup fails.

When the task lookup fails, the function also checks whether the timer is still enqueued and issues a warning if that's the case. Unfortunately there is nothing which can be done about it, but as the task is already not longer visible the timer should not be accessed anymore. This check also requires memory ordering, which is not provided when the first lookup fails. To achieve that the check is preceeded by a smp_rmb() which pairs with the smp_wmb() in write_seqlock() in __exit_signal(). That ensures that the stores in posix_cpu_timers*_exit() are visible.

The history of the non-leader exec() issue goes back to the early days of posix CPU timers, which stored a pointer to the group leader task in the timer. That obviously fails when a non-leader exec() switches the leader. commit e0a70217107e ("posix-cpu-timers: workaround to suppress the problems with mt exec") added a temporary workaround for that in 2010 which surv ---truncated---

Detalles técnicos trazas, registros y código del informe original
 sys_timer_delete()			exec()
   posix_cpu_timer_del()
   // Observes old leader
   p = pid_task(pid, pid_type);		de_thread()
   					  switch_leader();
					  release_task(old_leader)
					    __exit_signal(old_leader)
					      sighand = lock(old_leader, sighand);
					      posix_cpu_timers*_exit();
   sighand = lock_task_sighand(p)	      unhash_task(old_leader);
     sh = lock(p, sighand)	    	      old_leader->sighand = NULL;
					      unlock(sighand);
     (p->sighand == NULL)
	unlock(sh)
	return NULL;

   // Returns without action
   if(!sighand)
      return 0;
   free_posix_timer();

   posix_cpu_timer_del(tmr)
					__exit_signal(p)
					  posix_cpu_timers*_exit(p);
					  unhash_task(p);
					  p->sighand = NULL;
     sh = lock_task_sighand(p)
        sighand = p->sighand;
	if (!sighand)
	    return NULL;
	lock(sighand);

     if (!sh)
	WARN_ON_ONCE(timer_queued(tmr));

  1) Changing the store in __exit_signal() to smp_store_release().

  2) Adding a smp_acquire__after_ctrl_dep() into the !sighand path
     of lock_task_sighand().

  3) Creating a helper function for looking up the task and locking sighand
     which does not return when sighand == NULL. Instead it retries the
     task lookup and only if that fails it gives up.

  4) Using that helper in the three affected functions.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad de condición de carrera (race condition) en el kernel Linux que requiere acceso local (AV:L, PR:L) para explotar, permitiendo escalada de privilegios (I:H, A:H). El UAF resultante causa DoS e información sensible en memoria del kernel.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

User TrainingUser Account ManagementThreat Intelligence ProgramFilter Network TrafficExecution PreventionApplication Isolation and Sandboxing

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux KernelAI

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-64560",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.8,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 1.8
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
              "lessThan": "67aa823e3e8c229c6d374df79c804f6721cb83b6",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
              "lessThan": "d8bcb28abad857f1415da7656f19b2ada90af04f",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
              "lessThan": "cc35ddbc497311e0b6b9a6a6a4f4d1217d6ab1aa",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
              "lessThan": "12a891c773aeb5823d63dbd0cb2ab931d6c21c9b",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
              "lessThan": "e74443f5db0037c556ef436fa64b88bf4ea08f83",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
              "lessThan": "6a7ecc25abe6f0fecc6e62a05096987200edbd02",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
              "lessThan": "ad1cafa1bdaa71da85d71cac053838bbe97852b6",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
              "lessThan": "920f893f735e92ba3a1cd9256899a186b161928d",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "kernel/exit.c",
            "kernel/signal.c",
            "kernel/time/posix-cpu-timers.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.7"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "5.7",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "5.10.262",
              "versionType": "semver",
              "lessThanOrEqual": "5.10.*"
            },
            {
              "status": "unaffected",
              "version": "5.15.213",
              "versionType": "semver",
              "lessThanOrEqual": "5.15.*"
            },
            {
              "status": "unaffected",
              "version": "6.1.180",
              "versionType": "semver",
              "lessThanOrEqual": "6.1.*"
            },
            {
              "status": "unaffected",
              "version": "6.6.147",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.100",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.18.41",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "status": "unaffected",
              "version": "7.1.5",
              "versionType": "semver",
              "lessThanOrEqual": "7.1.*"
            },
            {
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "kernel/exit.c",
            "kernel/signal.c",
            "kernel/time/posix-cpu-timers.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    },
    {
      "source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
      "affectedData": [
        {
          "vendor": "Siemens",
          "product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP",
          "versions": [
            {
              "status": "affected",
              "version": "V3.1.6",
              "lessThan": "*",
              "versionType": "custom"
            }
          ],
          "defaultStatus": "unknown"
        },
        {
          "vendor": "Siemens",
          "product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP",
          "versions": [
            {
              "status": "affected",
              "version": "V3.1.6",
              "lessThan": "*",
              "versionType": "custom"
            }
          ],
          "defaultStatus": "unknown"
        },
        {
          "vendor": "Siemens",
          "product": "SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP",
          "versions": [
            {
              "status": "affected",
              "version": "V3.1.6",
              "lessThan": "*",
              "versionType": "custom"
            }
          ],
          "defaultStatus": "unknown"
        },
        {
          "vendor": "Siemens",
          "product": "SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP",
          "versions": [
            {
              "status": "affected",
              "version": "V3.1.6",
              "lessThan": "*",
              "versionType": "custom"
            }
          ],
          "defaultStatus": "unknown"
        },
        {
          "vendor": "Siemens",
          "product": "SIPLUS S7-1500 CPU 1518-4 PN/DP MFP",
          "versions": [
            {
              "status": "affected",
              "version": "V3.1.6",
              "lessThan": "*",
              "versionType": "custom"
            }
          ],
          "defaultStatus": "unknown"
        }
      ]
    }
  ],
  "published": "2026-07-29T17:16:53.637",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/12a891c773aeb5823d63dbd0cb2ab931d6c21c9b",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/67aa823e3e8c229c6d374df79c804f6721cb83b6",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/6a7ecc25abe6f0fecc6e62a05096987200edbd02",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/920f893f735e92ba3a1cd9256899a186b161928d",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/ad1cafa1bdaa71da85d71cac053838bbe97852b6",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/cc35ddbc497311e0b6b9a6a6a4f4d1217d6ab1aa",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/d8bcb28abad857f1415da7656f19b2ada90af04f",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/e74443f5db0037c556ef436fa64b88bf4ea08f83",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
      "source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nposix-cpu-timers: Prevent UAF caused by non-leader exec() race\n\nWongi and Jungwoo decoded and reported a non-leader exec() related race\nwhich can result in an UAF:\n\n sys_timer_delete()\t\t\texec()\n   posix_cpu_timer_del()\n   // Observes old leader\n   p = pid_task(pid, pid_type);\t\tde_thread()\n   \t\t\t\t\t  switch_leader();\n\t\t\t\t\t  release_task(old_leader)\n\t\t\t\t\t    __exit_signal(old_leader)\n\t\t\t\t\t      sighand = lock(old_leader, sighand);\n\t\t\t\t\t      posix_cpu_timers*_exit();\n   sighand = lock_task_sighand(p)\t      unhash_task(old_leader);\n     sh = lock(p, sighand)\t    \t      old_leader->sighand = NULL;\n\t\t\t\t\t      unlock(sighand);\n     (p->sighand == NULL)\n\tunlock(sh)\n\treturn NULL;\n\n   // Returns without action\n   if(!sighand)\n      return 0;\n   free_posix_timer();\n\nThis is \"harmless\" unless the deleted timer was armed and enqueued in\np->signal because on exec() a TGID targeted timer is inherited.\n\nAs sys_timer_delete() freed the underlying posix timer object\nrun_posix_cpu_timers() or any timerqueue related add/delete operations on\nother timers will access the freed object's timerqueue node, which results\nin an UAF.\n\nThere is a similar problem vs. posix_cpu_timer_set(). For regular posix\ntimers it just transiently returns -ESRCH to user space, but for the use\ncase in do_cpu_nanosleep() it's the same UAF just that the k_itimer is\nallocated on the stack.\n\nAlso posix_cpu_timer_rearm() fails to rearm the timer, which means it stops\nto expire.\n\nWhile debating solutions Frederic pointed out another problem:\n\n   posix_cpu_timer_del(tmr)\n\t\t\t\t\t__exit_signal(p)\n\t\t\t\t\t  posix_cpu_timers*_exit(p);\n\t\t\t\t\t  unhash_task(p);\n\t\t\t\t\t  p->sighand = NULL;\n     sh = lock_task_sighand(p)\n        sighand = p->sighand;\n\tif (!sighand)\n\t    return NULL;\n\tlock(sighand);\n\n     if (!sh)\n\tWARN_ON_ONCE(timer_queued(tmr));\n\nOn weakly ordered architectures it is not guaranteed that\nposix_cpu_timer_del() will observe the stores in posix_cpu_timers*_exit()\nwhen p->sighand is observed as NULL, which means the WARN() can be a false\npositive.\n\nSolve these issues by:\n\n  1) Changing the store in __exit_signal() to smp_store_release().\n\n  2) Adding a smp_acquire__after_ctrl_dep() into the !sighand path\n     of lock_task_sighand().\n\n  3) Creating a helper function for looking up the task and locking sighand\n     which does not return when sighand == NULL. Instead it retries the\n     task lookup and only if that fails it gives up.\n\n  4) Using that helper in the three affected functions.\n\n#1/#2 ensures that the reader side which observes sighand == NULL also\nobserves all preceeding stores, i.e. the stores in posix_cpu_timers*_exit()\nand the ones in unhash_task().\n\n#3 ensures that the above described non-leader exec() situation is handled\ngracefully. When the task lookup returns the old leader, but sighand ==\nNULL then it retries. In the non-leader exec() case the subsequent task\nlookup will observe the new leader due to #1/#2. In normal exit() scenarios\nthe subsequent lookup fails.\n\nWhen the task lookup fails, the function also checks whether the timer is\nstill enqueued and issues a warning if that's the case. Unfortunately there\nis nothing which can be done about it, but as the task is already not\nlonger visible the timer should not be accessed anymore. This check also\nrequires memory ordering, which is not provided when the first lookup\nfails. To achieve that the check is preceeded by a smp_rmb() which pairs\nwith the smp_wmb() in write_seqlock() in __exit_signal(). That ensures that\nthe stores in posix_cpu_timers*_exit() are visible.\n\nThe history of the non-leader exec() issue goes back to the early days of\nposix CPU timers, which stored a pointer to the group leader task in the\ntimer. That obviously fails when a non-leader exec() switches the leader.\ncommit e0a70217107e (\"posix-cpu-timers: workaround to suppress the problems\nwith mt exec\") added a temporary workaround for that in 2010 which surv\n---truncated---"
    }
  ],
  "lastModified": "2026-09-08T09:18:20.357",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}