CVE-2026-63809 (GCVE-0-2026-63809)

Vulnerability from cvelistv5 – Published: 2026-07-19 12:02 – Updated: 2026-07-20 13:40
VLAI
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)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
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)
Create a notification for this product.
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-rc1 , ≤ * (original_commit_for_fix)
Create a notification for this product.
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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."
        }
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            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
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        "dateUpdated": "2026-07-20T13:40:18.658Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e"
        },
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          "url": "https://git.kernel.org/stable/c/77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2"
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          "url": "https://git.kernel.org/stable/c/838fe9c28121777c59a9406710a68fcf77bb8017"
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          "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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    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63809",
    "datePublished": "2026-07-19T12:02:11.905Z",
    "dateReserved": "2026-07-19T07:54:57.013Z",
    "dateUpdated": "2026-07-20T13:40:18.658Z",
    "state": "PUBLISHED"
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  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-63809",
      "date": "2026-07-21",
      "epss": "0.00146",
      "percentile": "0.04299"
    },
    "microsoft_vex": {
      "current_release_date": "2026-07-20T14:43:51.000Z",
      "cve": "CVE-2026-63809",
      "id": "msrc_CVE-2026-63809",
      "initial_release_date": "2026-07-20T01:04:44.000Z",
      "product_status:known_affected": "1",
      "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": "2"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-63809\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-07-19T12:16:53.757\",\"lastModified\":\"2026-07-20T15:16:47.803\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"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.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"kernel/bpf/cgroup.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"b7925acd82926ebbf94a0f0783a3961f4e558856\",\"lessThan\":\"d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"4508943794efdd94171549c0bd52810e2f4ad9fe\",\"lessThan\":\"77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"4508943794efdd94171549c0bd52810e2f4ad9fe\",\"lessThan\":\"e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"4508943794efdd94171549c0bd52810e2f4ad9fe\",\"lessThan\":\"81fc9a13acae99966232f0e055eb2e445263b89a\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"4508943794efdd94171549c0bd52810e2f4ad9fe\",\"lessThan\":\"838fe9c28121777c59a9406710a68fcf77bb8017\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"4508943794efdd94171549c0bd52810e2f4ad9fe\",\"lessThan\":\"65bd0c0afb0e1bf3287458e342429b069624f7d4\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"4508943794efdd94171549c0bd52810e2f4ad9fe\",\"lessThan\":\"70df4de46577fab5e25418f014583155a147c902\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"4508943794efdd94171549c0bd52810e2f4ad9fe\",\"lessThan\":\"4c21b5927d4364bfe7365f2700da5fea0ed0d004\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"66258ab303588936ee1ee0794d9a271be24f73cb\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5.10.20\",\"lessThan\":\"5.10.260\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"5.11.3\",\"lessThan\":\"5.12\",\"versionType\":\"semver\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"kernel/bpf/cgroup.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"5.12\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"5.12\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.10.260\",\"lessThanOrEqual\":\"5.10.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.211\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.1.177\",\"lessThanOrEqual\":\"6.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.144\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.95\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.38\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1.3\",\"lessThanOrEqual\":\"7.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2-rc1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":7.8,\"baseSeverity\":\"HIGH\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":5.9}]},\"references\":[{\"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\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "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"
    }
  }
}



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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.


Detection rules are retrieved from Rulezet.