CVE-2026-63809 (GCVE-0-2026-63809)
Vulnerability from cvelistv5 – Published: 2026-07-19 12:02 – Updated: 2026-08-17 04:51
VLAI
EPSS
VEX
Title
bpf: use kvfree() for replaced sysctl write buffer
Summary
In the Linux kernel, the following vulnerability has been resolved:
bpf: use kvfree() for replaced sysctl write buffer
proc_sys_call_handler() allocates its temporary sysctl buffer with
kvzalloc() and passes it to __cgroup_bpf_run_filter_sysctl(). Since
kvzalloc() may fall back to vmalloc() for large allocations, freeing
that buffer with kfree() is wrong and can corrupt memory.
Use kvfree() to safely handle both kmalloc and kvzalloc()/vmalloc
allocations.
The bug was first flagged by an experimental analysis tool we are
developing for kernel memory-management bugs while analyzing
v6.13-rc1. The tool is still under development and is not yet publicly
available. Manual inspection confirms that the bug is still
present in v7.1-rc5.
Reproduced the bug based on v7.1-rc4 in a QEMU x86_64 guest booted with
KASAN and CONFIG_FAILSLAB enabled. To exercise the replacement path, the
test tree also included the accompanying fix for the stale ret == 1
check in __cgroup_bpf_run_filter_sysctl(). The reproducer confines
failslab injections to the proc_sys_call_handler() range, uses
stacktrace-depth=32, and injects fail-nth=1 while writing 8191 bytes to
/proc/sys/kernel/domainname from a task in the target cgroup. Under
that setup, fail-nth=1 triggered the fault:
BUG: unable to handle page fault for address: ffffeb0200024d48
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 SMP KASAN NOPTI
CPU: 2 UID: 0 PID: 209 Comm: repro_proc_sys_ Not tainted 7.1.0-rc4-00686-g97625979a5d4 PREEMPT(lazy)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
RIP: 0010:kfree+0x6e/0x510
...
Call Trace:
<TASK>
? __cgroup_bpf_run_filter_sysctl+0x626/0xc30
__cgroup_bpf_run_filter_sysctl+0x74d/0xc30
? __pfx___cgroup_bpf_run_filter_sysctl+0x10/0x10
? srso_return_thunk+0x5/0x5f
? __kvmalloc_node_noprof+0x345/0x870
? proc_sys_call_handler+0x250/0x480
? srso_return_thunk+0x5/0x5f
proc_sys_call_handler+0x3a2/0x480
? __pfx_proc_sys_call_handler+0x10/0x10
? srso_return_thunk+0x5/0x5f
? selinux_file_permission+0x39f/0x500
? srso_return_thunk+0x5/0x5f
? lock_is_held_type+0x9e/0x120
vfs_write+0x98e/0x1000
...
</TASK>
With this fix applied on top of the same test setup, rerunning the
reproducer with fail-nth=1 yields no corresponding Oops reports.
Severity
7.8 (High)
Assigner
References
8 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
b7925acd82926ebbf94a0f0783a3961f4e558856 , < d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e
(git)
Affected: 4508943794efdd94171549c0bd52810e2f4ad9fe , < 77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2 (git) Affected: 4508943794efdd94171549c0bd52810e2f4ad9fe , < e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2 (git) Affected: 4508943794efdd94171549c0bd52810e2f4ad9fe , < 81fc9a13acae99966232f0e055eb2e445263b89a (git) Affected: 4508943794efdd94171549c0bd52810e2f4ad9fe , < 838fe9c28121777c59a9406710a68fcf77bb8017 (git) Affected: 4508943794efdd94171549c0bd52810e2f4ad9fe , < 65bd0c0afb0e1bf3287458e342429b069624f7d4 (git) Affected: 4508943794efdd94171549c0bd52810e2f4ad9fe , < 70df4de46577fab5e25418f014583155a147c902 (git) Affected: 4508943794efdd94171549c0bd52810e2f4ad9fe , < 4c21b5927d4364bfe7365f2700da5fea0ed0d004 (git) Affected: 66258ab303588936ee1ee0794d9a271be24f73cb (git) Affected: 5.10.20 , < 5.10.260 (semver) Affected: 5.11.3 , < 5.12 (semver) |
guessed | |
| Linux | Linux |
Affected:
5.12
Unaffected: 0 , < 5.12 (semver) Unaffected: 5.10.260 , ≤ 5.10.* (semver) Unaffected: 5.15.211 , ≤ 5.15.* (semver) Unaffected: 6.1.177 , ≤ 6.1.* (semver) Unaffected: 6.6.144 , ≤ 6.6.* (semver) Unaffected: 6.12.95 , ≤ 6.12.* (semver) Unaffected: 6.18.38 , ≤ 6.18.* (semver) Unaffected: 7.1.3 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix) |
guessed |
{
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{
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},
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"version": "5.10.260",
"versionType": "semver"
},
{
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},
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},
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},
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"status": "unaffected",
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},
{
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"version": "7.1.3",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: use kvfree() for replaced sysctl write buffer\n\nproc_sys_call_handler() allocates its temporary sysctl buffer with\nkvzalloc() and passes it to __cgroup_bpf_run_filter_sysctl(). Since\nkvzalloc() may fall back to vmalloc() for large allocations, freeing\nthat buffer with kfree() is wrong and can corrupt memory.\n\nUse kvfree() to safely handle both kmalloc and kvzalloc()/vmalloc\nallocations.\n\nThe bug was first flagged by an experimental analysis tool we are\ndeveloping for kernel memory-management bugs while analyzing\nv6.13-rc1. The tool is still under development and is not yet publicly\navailable. Manual inspection confirms that the bug is still\npresent in v7.1-rc5.\n\nReproduced the bug based on v7.1-rc4 in a QEMU x86_64 guest booted with\nKASAN and CONFIG_FAILSLAB enabled. To exercise the replacement path, the\ntest tree also included the accompanying fix for the stale ret == 1\ncheck in __cgroup_bpf_run_filter_sysctl(). The reproducer confines\nfailslab injections to the proc_sys_call_handler() range, uses\nstacktrace-depth=32, and injects fail-nth=1 while writing 8191 bytes to\n/proc/sys/kernel/domainname from a task in the target cgroup. Under\nthat setup, fail-nth=1 triggered the fault:\n\n BUG: unable to handle page fault for address: ffffeb0200024d48\n #PF: supervisor read access in kernel mode\n #PF: error_code(0x0000) - not-present page\n PGD 0 P4D 0\n Oops: Oops: 0000 SMP KASAN NOPTI\n CPU: 2 UID: 0 PID: 209 Comm: repro_proc_sys_ Not tainted 7.1.0-rc4-00686-g97625979a5d4 PREEMPT(lazy)\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014\n RIP: 0010:kfree+0x6e/0x510\n ...\n Call Trace:\n \u003cTASK\u003e\n ? __cgroup_bpf_run_filter_sysctl+0x626/0xc30\n __cgroup_bpf_run_filter_sysctl+0x74d/0xc30\n ? __pfx___cgroup_bpf_run_filter_sysctl+0x10/0x10\n ? srso_return_thunk+0x5/0x5f\n ? __kvmalloc_node_noprof+0x345/0x870\n ? proc_sys_call_handler+0x250/0x480\n ? srso_return_thunk+0x5/0x5f\n proc_sys_call_handler+0x3a2/0x480\n ? __pfx_proc_sys_call_handler+0x10/0x10\n ? srso_return_thunk+0x5/0x5f\n ? selinux_file_permission+0x39f/0x500\n ? srso_return_thunk+0x5/0x5f\n ? lock_is_held_type+0x9e/0x120\n vfs_write+0x98e/0x1000\n ...\n \u003c/TASK\u003e\n\nWith this fix applied on top of the same test setup, rerunning the\nreproducer with fail-nth=1 yields no corresponding Oops reports."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The bug is reached only via a local write() to /proc/sys/* through proc_sys_call_handler() \u2192 BPF_CGROUP_RUN_PROG_SYSCTL() \u2192 __cgroup_bpf_run_filter_sysctl(); there is no network, adjacent-radio, or physical-device entry point.\nAC:L - An attacker controls all prerequisites: they can mount/join a cgroup, load and attach a cgroup/sysctl BPF program that calls bpf_sysctl_set_new_value(), issue a \u003ePAGE_SIZE sysctl write, and induce kmalloc failure (e.g., memory pressure) so kvzalloc() falls back to vmalloc and the wrong kfree() path is taken.\nPR:L - In a user+network namespace (unshare -Urn), CAP_NET_ADMIN grants write access to /proc/sys/net/* sysctls, and CAP_BPF plus CAP_NET_ADMIN suffice to load/attach BPF_PROG_TYPE_CGROUP_SYSCTL; cgroup management is available with namespace CAP_SYS_ADMIN, without init-namespace root.\nUI:N - Exploitation is fully attacker-driven through syscalls (write, bpf) and requires no victim interaction.\nS:U - Impact is kernel memory corruption and potential privilege escalation within the same kernel/host security boundary, not a cross-boundary escape such as VM or IOMMU bypass.\nC:H - Calling kfree() on a vmalloc-backed kvzalloc() buffer corrupts slab allocator metadata and can be leveraged for arbitrary kernel memory disclosure, not merely a bounded leak.\nI:H - Invalid kfree() of vmalloc memory is a heap corruption primitive that can corrupt slab freelists and be developed into arbitrary kernel writes or code execution.\nA:H - The reproducer triggers an immediate kernel oops/page fault in kfree(), and the underlying allocator corruption can also cause panics, hangs, or repeated crashes."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-17T04:51:15.528Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"references": [
{
"url": "https://git.kernel.org/stable/c/d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e"
},
{
"url": "https://git.kernel.org/stable/c/77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2"
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},
{
"url": "https://git.kernel.org/stable/c/81fc9a13acae99966232f0e055eb2e445263b89a"
},
{
"url": "https://git.kernel.org/stable/c/838fe9c28121777c59a9406710a68fcf77bb8017"
},
{
"url": "https://git.kernel.org/stable/c/65bd0c0afb0e1bf3287458e342429b069624f7d4"
},
{
"url": "https://git.kernel.org/stable/c/70df4de46577fab5e25418f014583155a147c902"
},
{
"url": "https://git.kernel.org/stable/c/4c21b5927d4364bfe7365f2700da5fea0ed0d004"
}
],
"title": "bpf: use kvfree() for replaced sysctl write buffer",
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"cveId": "CVE-2026-63809",
"datePublished": "2026-07-19T12:02:11.905Z",
"dateReserved": "2026-07-19T07:54:57.013Z",
"dateUpdated": "2026-08-17T04:51:15.528Z",
"state": "PUBLISHED"
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"vulnerability-lookup:meta": {
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"cve": "CVE-2026-63809",
"date": "2026-09-18",
"epss": "0.00154",
"percentile": "0.04932"
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"microsoft_vex": {
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"cve": "CVE-2026-63809",
"id": "msrc_CVE-2026-63809",
"initial_release_date": "2026-07-20T01:04:44.000Z",
"product_status:fixed": "1",
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"source": "Microsoft CSAF VEX",
"status": "final",
"title": "bpf: use kvfree() for replaced sysctl write buffer",
"url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-63809.json",
"version": "6"
},
"nvd": {
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},
{
"lessThan": "5.12",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "5.10.260",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.211",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.177",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.144",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.95",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.38",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.3",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"cveTags": [],
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{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: use kvfree() for replaced sysctl write buffer\n\nproc_sys_call_handler() allocates its temporary sysctl buffer with\nkvzalloc() and passes it to __cgroup_bpf_run_filter_sysctl(). Since\nkvzalloc() may fall back to vmalloc() for large allocations, freeing\nthat buffer with kfree() is wrong and can corrupt memory.\n\nUse kvfree() to safely handle both kmalloc and kvzalloc()/vmalloc\nallocations.\n\nThe bug was first flagged by an experimental analysis tool we are\ndeveloping for kernel memory-management bugs while analyzing\nv6.13-rc1. The tool is still under development and is not yet publicly\navailable. Manual inspection confirms that the bug is still\npresent in v7.1-rc5.\n\nReproduced the bug based on v7.1-rc4 in a QEMU x86_64 guest booted with\nKASAN and CONFIG_FAILSLAB enabled. To exercise the replacement path, the\ntest tree also included the accompanying fix for the stale ret == 1\ncheck in __cgroup_bpf_run_filter_sysctl(). The reproducer confines\nfailslab injections to the proc_sys_call_handler() range, uses\nstacktrace-depth=32, and injects fail-nth=1 while writing 8191 bytes to\n/proc/sys/kernel/domainname from a task in the target cgroup. Under\nthat setup, fail-nth=1 triggered the fault:\n\n BUG: unable to handle page fault for address: ffffeb0200024d48\n #PF: supervisor read access in kernel mode\n #PF: error_code(0x0000) - not-present page\n PGD 0 P4D 0\n Oops: Oops: 0000 SMP KASAN NOPTI\n CPU: 2 UID: 0 PID: 209 Comm: repro_proc_sys_ Not tainted 7.1.0-rc4-00686-g97625979a5d4 PREEMPT(lazy)\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014\n RIP: 0010:kfree+0x6e/0x510\n ...\n Call Trace:\n \u003cTASK\u003e\n ? __cgroup_bpf_run_filter_sysctl+0x626/0xc30\n __cgroup_bpf_run_filter_sysctl+0x74d/0xc30\n ? __pfx___cgroup_bpf_run_filter_sysctl+0x10/0x10\n ? srso_return_thunk+0x5/0x5f\n ? __kvmalloc_node_noprof+0x345/0x870\n ? proc_sys_call_handler+0x250/0x480\n ? srso_return_thunk+0x5/0x5f\n proc_sys_call_handler+0x3a2/0x480\n ? __pfx_proc_sys_call_handler+0x10/0x10\n ? srso_return_thunk+0x5/0x5f\n ? selinux_file_permission+0x39f/0x500\n ? srso_return_thunk+0x5/0x5f\n ? lock_is_held_type+0x9e/0x120\n vfs_write+0x98e/0x1000\n ...\n \u003c/TASK\u003e\n\nWith this fix applied on top of the same test setup, rerunning the\nreproducer with fail-nth=1 yields no corresponding Oops reports."
}
],
"id": "CVE-2026-63809",
"lastModified": "2026-08-17T05:17:17.913",
"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"
}
]
},
"published": "2026-07-19T12:16:53.757",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/4c21b5927d4364bfe7365f2700da5fea0ed0d004"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/65bd0c0afb0e1bf3287458e342429b069624f7d4"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/70df4de46577fab5e25418f014583155a147c902"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/81fc9a13acae99966232f0e055eb2e445263b89a"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/838fe9c28121777c59a9406710a68fcf77bb8017"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Awaiting Analysis"
}
},
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-07-20T17:11:04+00:00",
"cve": "CVE-2026-63809",
"id": "CVE-2026-63809",
"initial_release_date": "2026-07-19T00:00:00+00:00",
"product_status:known_affected": "184",
"product_status:known_not_affected": "90",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: bpf: use kvfree() for replaced sysctl write buffer",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63809.json",
"version": "3"
},
"suse_vex": {
"aggregate_severity": "moderate",
"current_release_date": "2026-09-10T16:49:44Z",
"cve": "CVE-2026-63809",
"id": "CVE-2026-63809",
"initial_release_date": "2026-07-19T17:34:56Z",
"product_status:first_fixed": "2",
"product_status:known_affected": "511",
"product_status:known_not_affected": "193",
"product_status:recommended": "254",
"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2026-63809",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-63809.json",
"version": "17"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
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.
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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.
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