CVE-2026-98642
Status: ReceivedUnscored—
Severity—Unscored
Exploitation probability0.17 %higher than 6% of CVEs
Active exploitationNonot in the CISA catalog
Public exploitNot knownno public code found
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk
Syzkaller repeatedly triggered UAF splats related to nodes in waiting_for_gp_ttrace within the bpf memalloc:
The reason is that the UAF occurs after the RCU Tasks Trace GP expires: when the __free_rcu() callback runs, there is no synchronization protecting llist_del_all() against concurrent alloc_bulk() operating on waiting_for_gp_ttrace, leading to the race condition below:
In addition, there is also a theoretical race condition on the free_by_rcu_ttrace list.
Read full descriptionShow less
This race requires two preconditions: an in-flight Tasks Trace GP keeping c->call_rcu_ttrace_in_progress == 1, and concurrent cross-CPU frees repopulating c->free_by_rcu_ttrace with new nodes. Under these conditions, the following scenario triggers UAF:
Fix this by introducing a raw spinlock to synchronize the concurrent consumption on waiting_for_gp_ttrace and free_by_rcu_ttrace.
Technical details traces, logs and code from the original report
BUG: KASAN: slab-use-after-free in llist_del_first+0x85/0x110 lib/llist.c:61
Read of size 8 at addr ffff8881572cd080 by task syz.4.470/5112
...
llist_del_first+0x85/0x110 lib/llist.c:61
alloc_bulk+0x193/0x460 kernel/bpf/memalloc.c:229
bpf_mem_refill+0x386/0x560 kernel/bpf/memalloc.c:436
Freed by task 14:
...
__free_rcu kernel/bpf/memalloc.c:281 [inline]
__free_rcu_tasks_trace+0x48/0xd0 kernel/bpf/memalloc.c:291
rcu_tasks_invoke_cbs+0x1ec/0x3e0 kernel/rcu/tasks.h:571
rcu_tasks_one_gp+0x13d/0x220 kernel/rcu/tasks.h:621
rcu_tasks_kthread+0xf3/0x120 kernel/rcu/tasks.h:651
CPU0 CPU1
__free_rcu (RCU Tasks Trace callback)
alloc_bulk
llist_del_first(&c->waiting_for_gp_ttrace)
entry = smp_load_acquire(&head->first);
do {
if (entry == NULL)
return NULL;
free_all(llist_del_all(&c->waiting_for_gp_ttrace))
llist_for_each_safe(pos, t, llnode)
free_one(pos);
next = READ_ONCE(entry->next); <-- trigger UAF
} while (!try_cmpxchg(&head->first, &entry, next));
// CPU0
// irq work is still busy (on PREEMPT_RT)
alloc_bulk()
llist_del_first(&c->free_by_rcu_ttrace)
entry = smp_load_acquire(&head->first);
do {
if (entry == NULL)
return NULL;
// CPU1
bpf_mem_alloc_destroy()
WRITE_ONCE(c->draining, true)
// wait for CPU0
irq_work_sync()
// CPU2
do_call_rcu_ttrace(tgt(CPU0))
if (c->draining) {
llist_del_all(&c->free_by_rcu_ttrace)
free_all()
}
// CPU0 continue
next = READ_ONCE(entry->next); <-- trigger UAF
while (!try_cmpxchg(&head->first, &entry, next));CVSS
NVD hasn't assigned a CVSS score to this CVE (common since the April 2026 policy change).
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days
- 0.17 %
- Percentile among all scored CVEs
- 6
- Score date
- 10/20/2026
EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).
Affected technologies (1)
⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.
References
Show 4 references
Raw JSON (NVD)
Show
{
"id": "CVE-2026-98642",
"cveTags": [],
"metrics": {},
"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": "04fabf00b4d3aff5d010ecb617001814e409e24a",
"lessThan": "a0e150a118025a05c8662c536ba2a865da86419c",
"versionType": "git"
},
{
"status": "affected",
"version": "04fabf00b4d3aff5d010ecb617001814e409e24a",
"lessThan": "1d6581b544a88cf4348c2fb60dcb50ad63f012da",
"versionType": "git"
},
{
"status": "affected",
"version": "04fabf00b4d3aff5d010ecb617001814e409e24a",
"lessThan": "f101602415fb39a58941bec444df65634d5a6844",
"versionType": "git"
},
{
"status": "affected",
"version": "04fabf00b4d3aff5d010ecb617001814e409e24a",
"lessThan": "1c21452d02eec2f008e2c5535820f85adbd7587a",
"versionType": "git"
}
],
"programFiles": [
"kernel/bpf/memalloc.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "6.6"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "6.6",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "6.12.112",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.55",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.9",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"kernel/bpf/memalloc.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-10-18T16:17:17.367",
"references": [
{
"url": "https://git.kernel.org/stable/c/1c21452d02eec2f008e2c5535820f85adbd7587a",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/1d6581b544a88cf4348c2fb60dcb50ad63f012da",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/a0e150a118025a05c8662c536ba2a865da86419c",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/f101602415fb39a58941bec444df65634d5a6844",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk\n\nSyzkaller repeatedly triggered UAF splats related to nodes in\nwaiting_for_gp_ttrace within the bpf memalloc:\n\nBUG: KASAN: slab-use-after-free in llist_del_first+0x85/0x110 lib/llist.c:61\nRead of size 8 at addr ffff8881572cd080 by task syz.4.470/5112\n ...\n llist_del_first+0x85/0x110 lib/llist.c:61\n alloc_bulk+0x193/0x460 kernel/bpf/memalloc.c:229\n bpf_mem_refill+0x386/0x560 kernel/bpf/memalloc.c:436\n\nFreed by task 14:\n ...\n __free_rcu kernel/bpf/memalloc.c:281 [inline]\n __free_rcu_tasks_trace+0x48/0xd0 kernel/bpf/memalloc.c:291\n rcu_tasks_invoke_cbs+0x1ec/0x3e0 kernel/rcu/tasks.h:571\n rcu_tasks_one_gp+0x13d/0x220 kernel/rcu/tasks.h:621\n rcu_tasks_kthread+0xf3/0x120 kernel/rcu/tasks.h:651\n\nThe reason is that the UAF occurs after the RCU Tasks Trace GP expires:\nwhen the __free_rcu() callback runs, there is no synchronization\nprotecting llist_del_all() against concurrent alloc_bulk() operating on\nwaiting_for_gp_ttrace, leading to the race condition below:\n\nCPU0 CPU1\n __free_rcu (RCU Tasks Trace callback)\nalloc_bulk\n llist_del_first(&c->waiting_for_gp_ttrace)\n entry = smp_load_acquire(&head->first);\n do {\n if (entry == NULL)\n return NULL;\n free_all(llist_del_all(&c->waiting_for_gp_ttrace))\n llist_for_each_safe(pos, t, llnode)\n free_one(pos);\n next = READ_ONCE(entry->next); <-- trigger UAF\n } while (!try_cmpxchg(&head->first, &entry, next));\n\nIn addition, there is also a theoretical race condition on the\nfree_by_rcu_ttrace list. This race requires two preconditions: an\nin-flight Tasks Trace GP keeping c->call_rcu_ttrace_in_progress == 1,\nand concurrent cross-CPU frees repopulating c->free_by_rcu_ttrace with\nnew nodes. Under these conditions, the following scenario triggers UAF:\n\n// CPU0\n// irq work is still busy (on PREEMPT_RT)\nalloc_bulk()\n llist_del_first(&c->free_by_rcu_ttrace)\n entry = smp_load_acquire(&head->first);\n do {\n if (entry == NULL)\n return NULL;\n\n // CPU1\n bpf_mem_alloc_destroy()\n WRITE_ONCE(c->draining, true)\n // wait for CPU0\n irq_work_sync()\n\n // CPU2\n do_call_rcu_ttrace(tgt(CPU0))\n if (c->draining) {\n llist_del_all(&c->free_by_rcu_ttrace)\n free_all()\n }\n\n// CPU0 continue\n next = READ_ONCE(entry->next); <-- trigger UAF\n while (!try_cmpxchg(&head->first, &entry, next));\n\nFix this by introducing a raw spinlock to synchronize the concurrent\nconsumption on waiting_for_gp_ttrace and free_by_rcu_ttrace."
}
],
"lastModified": "2026-10-19T10:19:28.443",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}