FKIE_CVE-2026-64560
Vulnerability from fkie_nvd - Published: 2026-07-29 17:16 - Updated: 2026-11-03 18:15
Severity
Summary
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:
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();
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.
Also posix_cpu_timer_rearm() fails to rearm the timer, which means it stops
to expire.
While debating solutions Frederic pointed out another problem:
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));
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) 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.
#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---
References
Impacted products
| Vendor | Product | Version |
|---|
{
"affected": [
{
"affectedData": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"kernel/exit.c",
"kernel/signal.c",
"kernel/time/posix-cpu-timers.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "67aa823e3e8c229c6d374df79c804f6721cb83b6",
"status": "affected",
"version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
"versionType": "git"
},
{
"lessThan": "d8bcb28abad857f1415da7656f19b2ada90af04f",
"status": "affected",
"version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
"versionType": "git"
},
{
"lessThan": "cc35ddbc497311e0b6b9a6a6a4f4d1217d6ab1aa",
"status": "affected",
"version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
"versionType": "git"
},
{
"lessThan": "12a891c773aeb5823d63dbd0cb2ab931d6c21c9b",
"status": "affected",
"version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
"versionType": "git"
},
{
"lessThan": "e74443f5db0037c556ef436fa64b88bf4ea08f83",
"status": "affected",
"version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
"versionType": "git"
},
{
"lessThan": "6a7ecc25abe6f0fecc6e62a05096987200edbd02",
"status": "affected",
"version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
"versionType": "git"
},
{
"lessThan": "ad1cafa1bdaa71da85d71cac053838bbe97852b6",
"status": "affected",
"version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
"versionType": "git"
},
{
"lessThan": "920f893f735e92ba3a1cd9256899a186b161928d",
"status": "affected",
"version": "55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"kernel/exit.c",
"kernel/signal.c",
"kernel/time/posix-cpu-timers.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "5.7"
},
{
"lessThan": "5.7",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"version": "5.10.262",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.213",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.180",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.147",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.100",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.41",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.5",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"affectedData": [
{
"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": "V3.1.7",
"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 1518-4 PN/DP MFP",
"vendor": "Siemens",
"versions": [
{
"lessThan": "*",
"status": "affected",
"version": "V3.1.7",
"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": "V3.1.7",
"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": "V3.1.7",
"versionType": "custom"
}
]
},
{
"defaultStatus": "unknown",
"product": "SIMATIC S7-1500 TM MFP - GNU/Linux subsystem",
"vendor": "Siemens",
"versions": [
{
"lessThan": "*",
"status": "affected",
"version": "0",
"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"
}
]
},
{
"defaultStatus": "unknown",
"product": "SIPLUS S7-1500 CPU 1518-4 PN/DP MFP",
"vendor": "Siemens",
"versions": [
{
"lessThan": "*",
"status": "affected",
"version": "V3.1.7",
"versionType": "custom"
}
]
}
],
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"
}
],
"cveTags": [],
"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-\u003esighand = NULL;\n\t\t\t\t\t unlock(sighand);\n (p-\u003esighand == 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-\u003esignal 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\u0027s 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\u0027s 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-\u003esighand = NULL;\n sh = lock_task_sighand(p)\n sighand = p-\u003esighand;\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-\u003esighand 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\u0027s 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---"
}
],
"id": "CVE-2026-64560",
"lastModified": "2026-11-03T18:15:39.353",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.8,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"exploitabilityScore": 1.8,
"impactScore": 5.9,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2026-64560",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-10-16T15:42:46.237776Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-07-29T17:16:53.637",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"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": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
"url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
},
{
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
"url": "https://cert-portal.siemens.com/productcert/html/ssa-457936.html"
},
{
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
"url": "https://cert-portal.siemens.com/productcert/html/ssa-784472.html"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Awaiting Analysis",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-362"
}
],
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"type": "Secondary"
}
]
}
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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.
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- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
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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.
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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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.