Vulnerability-Lookup

GHSA-PR95-77XQ-3V99

Vulnerability from github – Published: 2026-10-06 09:31 – Updated: 2026-10-07 09:32

Details

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

exec: Cleanup POSIX timers right after de_thread()

A per-thread CPU timer holds a reference to the PID of the thread it is attached to and, while it is armed, its node is queued in that thread's posix_cputimers. The task is looked up by that PID.

When a non-leader thread exec()s, de_thread() changes which task owns that PID. pid_task(timer->it.cpu.pid, PIDTYPE_PID) then returns NULL, but the node is still queued on tsk, which is alive. timer_lock_sighand() takes a failed lookup to mean that the node is already dequeued, so it has nothing to undo.

begin_new_exec() calls posix_cpu_timers_exit(me) right after exec_task_namespaces() and that removes the leftover node, so the state normally stays invisible. But bprm->point_of_no_return is set before de_thread(), so if unshare_files(), set_mm_exe_file(), exec_mmap() or exec_task_namespaces() fails, the task dies before it gets there. exit_itimers() then frees the k_itimer while its node is still queued, and reaping tsk later erases that freed node from the rbtree.

In short:

  the non-leader thread B           the parent

timer_create(CLOCK_THREAD_CPUTIME_ID) timer_settime() arm_timer() // the node is queued on B execve() de_thread(B) exchange_tids(B, leader) // B's PID now belongs to the leader release_task(leader) __exit_signal(leader) posix_cpu_timers_exit(leader) // cleans leader's queue, not B's __unhash_process(leader) // that PID has no task anymore exec_mmap() mmap_read_lock_killable(old_mm) kill(B, SIGKILL) // -EINTR get_signal() do_exit() exit_itimers() posix_timer_delete() posix_cpu_timer_del() posix_timer_unhash_and_free() // freed while still queued wait4() release_task(B) posix_cpu_timers_exit(B) cleanup_timerqueue() timerqueue_del() // use-after-free

Move the POSIX timer cleanup right after de_thread() before any of the later failure conditions brings the task into do_exit().

[ tglx: Move the cleanup right after de_thread() ]

Severity

7.8 (High)


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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98260"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-06T09:18:15Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nexec: Cleanup POSIX timers right after de_thread()\n\nA per-thread CPU timer holds a reference to the PID of the thread it is\nattached to and, while it is armed, its node is queued in that thread\u0027s\nposix_cputimers. The task is looked up by that PID.\n\nWhen a non-leader thread exec()s, de_thread() changes which task owns\nthat PID. pid_task(timer-\u003eit.cpu.pid, PIDTYPE_PID) then returns NULL,\nbut the node is still queued on tsk, which is alive. timer_lock_sighand()\ntakes a failed lookup to mean that the node is already dequeued, so it\nhas nothing to undo.\n\nbegin_new_exec() calls posix_cpu_timers_exit(me) right after\nexec_task_namespaces() and that removes the leftover node, so the state\nnormally stays invisible. But bprm-\u003epoint_of_no_return is set before\nde_thread(), so if unshare_files(), set_mm_exe_file(), exec_mmap() or\nexec_task_namespaces() fails, the task dies before it gets there.\nexit_itimers() then frees the k_itimer while its node is still queued,\nand reaping tsk later erases that freed node from the rbtree.\n\nIn short:\n\n      the non-leader thread B           the parent\n\n  timer_create(CLOCK_THREAD_CPUTIME_ID)\n  timer_settime()\n    arm_timer()            // the node is queued on B\n  execve()\n    de_thread(B)\n      exchange_tids(B, leader)  // B\u0027s PID now belongs to the leader\n      release_task(leader)\n        __exit_signal(leader)\n          posix_cpu_timers_exit(leader)  // cleans leader\u0027s queue, not B\u0027s\n          __unhash_process(leader)  // that PID has no task anymore\n    exec_mmap()\n      mmap_read_lock_killable(old_mm)\n                                kill(B, SIGKILL)\n      // -EINTR\n  get_signal()\n    do_exit()\n      exit_itimers()\n        posix_timer_delete()\n          posix_cpu_timer_del()\n        posix_timer_unhash_and_free()  // freed while still queued\n                                wait4()\n                                  release_task(B)\n                                    posix_cpu_timers_exit(B)\n                                      cleanup_timerqueue()\n                                        timerqueue_del()  // use-after-free\n\nMove the POSIX timer cleanup right after de_thread() before any of the\nlater failure conditions brings the task into do_exit().\n\n[ tglx: Move the cleanup right after de_thread() ]",
  "id": "GHSA-pr95-77xq-3v99",
  "modified": "2026-10-07T09:32:14Z",
  "published": "2026-10-06T09:31:32Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98260"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6f1977cea3e85cd8ab55fb337d3e1725fe61d1ce"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/75aa08b93c65766040f9ca99f41ac85ad22596b6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/acb03d3881818581052924a9bbbe92b8741ed448"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d602877baf36c43c788a5f472c977e0be414029f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d9ae467e617ca29b825493a362bf0d75ad5f4ac3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-98260 (GCVE-0-2026-98260)

Vulnerability from cvelistv5 – Published: 2026-10-06 08:45 – Updated: 2026-10-07 06:49

Title

exec: Cleanup POSIX timers right after de_thread()

Summary

In the Linux kernel, the following vulnerability has been resolved: exec: Cleanup POSIX timers right after de_thread() A per-thread CPU timer holds a reference to the PID of the thread it is attached to and, while it is armed, its node is queued in that thread's posix_cputimers. The task is looked up by that PID. When a non-leader thread exec()s, de_thread() changes which task owns that PID. pid_task(timer->it.cpu.pid, PIDTYPE_PID) then returns NULL, but the node is still queued on tsk, which is alive. timer_lock_sighand() takes a failed lookup to mean that the node is already dequeued, so it has nothing to undo. begin_new_exec() calls posix_cpu_timers_exit(me) right after exec_task_namespaces() and that removes the leftover node, so the state normally stays invisible. But bprm->point_of_no_return is set before de_thread(), so if unshare_files(), set_mm_exe_file(), exec_mmap() or exec_task_namespaces() fails, the task dies before it gets there. exit_itimers() then frees the k_itimer while its node is still queued, and reaping tsk later erases that freed node from the rbtree. In short: the non-leader thread B the parent timer_create(CLOCK_THREAD_CPUTIME_ID) timer_settime() arm_timer() // the node is queued on B execve() de_thread(B) exchange_tids(B, leader) // B's PID now belongs to the leader release_task(leader) __exit_signal(leader) posix_cpu_timers_exit(leader) // cleans leader's queue, not B's __unhash_process(leader) // that PID has no task anymore exec_mmap() mmap_read_lock_killable(old_mm) kill(B, SIGKILL) // -EINTR get_signal() do_exit() exit_itimers() posix_timer_delete() posix_cpu_timer_del() posix_timer_unhash_and_free() // freed while still queued wait4() release_task(B) posix_cpu_timers_exit(B) cleanup_timerqueue() timerqueue_del() // use-after-free Move the POSIX timer cleanup right after de_thread() before any of the later failure conditions brings the task into do_exit(). [ tglx: Move the cleanup right after de_thread() ]

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 CNA under the mitre root

CNA scorecard D 53/100 over 6664 records in the last 180 days details

References

5 references

URL	Tags
https://git.kernel.org/stable/c/6f1977cea3e85cd8a…
https://git.kernel.org/stable/c/d9ae467e617ca29b8…
https://git.kernel.org/stable/c/75aa08b93c6576604…
https://git.kernel.org/stable/c/d602877baf36c43c7…
https://git.kernel.org/stable/c/acb03d38818185810…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 , < 6f1977cea3e85cd8ab55fb337d3e1725fe61d1ce (git) Affected: 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 , < d9ae467e617ca29b825493a362bf0d75ad5f4ac3 (git) Affected: 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 , < 75aa08b93c65766040f9ca99f41ac85ad22596b6 (git) Affected: 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 , < d602877baf36c43c788a5f472c977e0be414029f (git) Affected: 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 , < acb03d3881818581052924a9bbbe92b8741ed448 (git)
Linux	Linux	Affected: 5.7 Unaffected: 0 , < 5.7 (semver) Unaffected: 6.6.158 , ≤ 6.6.* (semver) Unaffected: 6.12.112 , ≤ 6.12.* (semver) Unaffected: 6.18.54 , ≤ 6.18.* (semver) Unaffected: 7.2.8 , ≤ 7.2.* (semver) Unaffected: 7.3-rc4 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/exec.c"
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              "versionType": "git"
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          "versions": [
            {
              "status": "affected",
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.12.112",
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            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.54",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.8",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc4",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nexec: Cleanup POSIX timers right after de_thread()\n\nA per-thread CPU timer holds a reference to the PID of the thread it is\nattached to and, while it is armed, its node is queued in that thread\u0027s\nposix_cputimers. The task is looked up by that PID.\n\nWhen a non-leader thread exec()s, de_thread() changes which task owns\nthat PID. pid_task(timer-\u003eit.cpu.pid, PIDTYPE_PID) then returns NULL,\nbut the node is still queued on tsk, which is alive. timer_lock_sighand()\ntakes a failed lookup to mean that the node is already dequeued, so it\nhas nothing to undo.\n\nbegin_new_exec() calls posix_cpu_timers_exit(me) right after\nexec_task_namespaces() and that removes the leftover node, so the state\nnormally stays invisible. But bprm-\u003epoint_of_no_return is set before\nde_thread(), so if unshare_files(), set_mm_exe_file(), exec_mmap() or\nexec_task_namespaces() fails, the task dies before it gets there.\nexit_itimers() then frees the k_itimer while its node is still queued,\nand reaping tsk later erases that freed node from the rbtree.\n\nIn short:\n\n      the non-leader thread B           the parent\n\n  timer_create(CLOCK_THREAD_CPUTIME_ID)\n  timer_settime()\n    arm_timer()            // the node is queued on B\n  execve()\n    de_thread(B)\n      exchange_tids(B, leader)  // B\u0027s PID now belongs to the leader\n      release_task(leader)\n        __exit_signal(leader)\n          posix_cpu_timers_exit(leader)  // cleans leader\u0027s queue, not B\u0027s\n          __unhash_process(leader)  // that PID has no task anymore\n    exec_mmap()\n      mmap_read_lock_killable(old_mm)\n                                kill(B, SIGKILL)\n      // -EINTR\n  get_signal()\n    do_exit()\n      exit_itimers()\n        posix_timer_delete()\n          posix_cpu_timer_del()\n        posix_timer_unhash_and_free()  // freed while still queued\n                                wait4()\n                                  release_task(B)\n                                    posix_cpu_timers_exit(B)\n                                      cleanup_timerqueue()\n                                        timerqueue_del()  // use-after-free\n\nMove the POSIX timer cleanup right after de_thread() before any of the\nlater failure conditions brings the task into do_exit().\n\n[ tglx: Move the cleanup right after de_thread() ]"
        }
      ],
      "metrics": [
        {
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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              "value": "AV:L - The bug needs local syscalls: timer_create(CLOCK_THREAD_CPUTIME_ID) and timer_settime() on a non-leader thread, then execve(). That thread\u0027s exec must fail after de_thread() in begin_new_exec() (e.g. exec_mmap() returning -EINTR on SIGKILL). No remote protocol carries any of this input.\nAC:L - The attacker controls both sides of the race. Their own parent sends SIGKILL while exec_mmap() waits on down_write_killable(exec_update_lock) or mmap_read_lock_killable(old_mm), and they can create that lock contention with their own CLONE_VM or /proc readers. No condition outside their control is needed.\nPR:L - Arming a thread CPU timer, calling execve and signalling one\u0027s own child are all available to any unprivileged user, with no capability checks on this path. A local unprivileged account is enough.\nUI:N - The attacker\u0027s own processes perform every step (timer arm, execve from a non-leader thread, SIGKILL, wait4 reap), so no victim action is needed.\nS:U - The memory corruption is inside the kernel that the attacker\u0027s process runs on. The outcome is a normal local privilege escalation, with no VM or sandbox boundary crossed.\nC:H - exit_itimers() frees the k_itimer while its cpu_timer node is still linked in the task\u0027s posix_cputimers rbtree. The freed slab object can be reclaimed with attacker-sprayed data, giving a use-after-free that can be turned into kernel memory disclosure.\nI:H - When release_task() reaps the task, posix_cpu_timers_exit() -\u003e cleanup_timerqueue() -\u003e timerqueue_del() calls rb_erase on the freed node and rewrites rbtree pointers in reclaimed memory. That is a use-after-free write which can be used for privilege escalation.\nA:H - The rbtree erase on freed memory corrupts kernel data and can oops or panic the kernel. Any unprivileged user can repeat it at will."
            }
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        }
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      "providerMetadata": {
        "dateUpdated": "2026-10-07T06:49:47.661Z",
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        },
        {
          "url": "https://git.kernel.org/stable/c/acb03d3881818581052924a9bbbe92b8741ed448"
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      ],
      "title": "exec: Cleanup POSIX timers right after de_thread()",
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    "datePublished": "2026-10-06T08:45:24.711Z",
    "dateReserved": "2026-09-25T10:25:14.332Z",
    "dateUpdated": "2026-10-07T06:49:47.661Z",
    "state": "PUBLISHED"
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
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.

Vulnerability timeline

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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.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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