{"id":"CVE-2026-63809","state":"PUBLISHED","title":"bpf: use kvfree() for replaced sysctl write buffer","description":"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   <TASK>\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   </TASK>\n\nWith this fix applied on top of the same test setup, rerunning the\nreproducer with fail-nth=1 yields no corresponding Oops reports.","publishedAt":"2026-07-19T12:02:11.905Z","updatedAt":"2026-10-19T20:07:48.575Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b7925acd82926ebbf94a0f0783a3961f4e558856","status":"affected","lessThan":"d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"81fc9a13acae99966232f0e055eb2e445263b89a","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"838fe9c28121777c59a9406710a68fcf77bb8017","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"65bd0c0afb0e1bf3287458e342429b069624f7d4","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"70df4de46577fab5e25418f014583155a147c902","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"4c21b5927d4364bfe7365f2700da5fea0ed0d004","versionType":"git"},{"version":"66258ab303588936ee1ee0794d9a271be24f73cb","status":"affected","versionType":"git"},{"version":"5.10.20","status":"affected","lessThan":"5.10.260","versionType":"semver"},{"version":"5.11.3","status":"affected","lessThan":"5.12","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/cgroup.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.12","versionType":"semver"},{"version":"5.10.260","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.211","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.177","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.144","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.95","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.38","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.3","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/cgroup.c"]}],"references":["https://git.kernel.org/stable/c/d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e","https://git.kernel.org/stable/c/77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2","https://git.kernel.org/stable/c/e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2","https://git.kernel.org/stable/c/81fc9a13acae99966232f0e055eb2e445263b89a","https://git.kernel.org/stable/c/838fe9c28121777c59a9406710a68fcf77bb8017","https://git.kernel.org/stable/c/65bd0c0afb0e1bf3287458e342429b069624f7d4","https://git.kernel.org/stable/c/70df4de46577fab5e25418f014583155a147c902","https://git.kernel.org/stable/c/4c21b5927d4364bfe7365f2700da5fea0ed0d004"],"weaknesses":["CWE-787"],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/63xxx/CVE-2026-63809.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63809","state":"PUBLISHED","datePublished":"2026-07-19T12:02:11.905Z","dateUpdated":"2026-10-19T20:07:48.575Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-19T07:54:57.013Z"},"containers":{"cna":{"title":"bpf: use kvfree() for replaced sysctl write buffer","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   <TASK>\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   </TASK>\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":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b7925acd82926ebbf94a0f0783a3961f4e558856","status":"affected","lessThan":"d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"81fc9a13acae99966232f0e055eb2e445263b89a","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"838fe9c28121777c59a9406710a68fcf77bb8017","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"65bd0c0afb0e1bf3287458e342429b069624f7d4","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"70df4de46577fab5e25418f014583155a147c902","versionType":"git"},{"version":"4508943794efdd94171549c0bd52810e2f4ad9fe","status":"affected","lessThan":"4c21b5927d4364bfe7365f2700da5fea0ed0d004","versionType":"git"},{"version":"66258ab303588936ee1ee0794d9a271be24f73cb","status":"affected","versionType":"git"},{"version":"5.10.20","status":"affected","lessThan":"5.10.260","versionType":"semver"},{"version":"5.11.3","status":"affected","lessThan":"5.12","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/cgroup.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.12","versionType":"semver"},{"version":"5.10.260","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.211","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.177","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.144","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.95","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.38","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.3","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/cgroup.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e"},{"url":"https://git.kernel.org/stable/c/77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2"},{"url":"https://git.kernel.org/stable/c/e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2"},{"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"}],"metrics":[{"cvssV3_1":{"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"},"scenarios":[{"lang":"en","value":"AV:L - The bug is reached only via a local write() to /proc/sys/* through proc_sys_call_handler() → BPF_CGROUP_RUN_PROG_SYSCTL() → __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 >PAGE_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":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-17T04:51:15.528Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.10.20","versionEndExcluding":"5.10.260"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"5.15.211"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.1.177"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.6.144"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.12.95"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.18.38"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"7.1.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"7.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-63809","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:31:06.256343Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-787","lang":"en","type":"CWE","description":"CWE-787 Out-of-bounds Write"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T20:07:48.575Z"}}]}}}