{"id":"CVE-2026-63809","title":"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_filt…","summary":"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_filt…","severity":"medium","published":"2026-07-19","updated":"2026-07-19","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-63809","references":[{"url":"https://git.kernel.org/stable/c/4c21b5927d4364bfe7365f2700da5fea0ed0d004","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/65bd0c0afb0e1bf3287458e342429b069624f7d4","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/70df4de46577fab5e25418f014583155a147c902","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/81fc9a13acae99966232f0e055eb2e445263b89a","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/838fe9c28121777c59a9406710a68fcf77bb8017","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63809.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-63809"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2502202"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-63809"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63809"},{"url":"https://lore.kernel.org/linux-cve-announce/2026071903-CVE-2026-63809-0af7@gregkh/T"}],"tags":["nvd","csaf","vex","red-hat"],"ingestedAt":"2026-07-20T09:37:17.825Z","epss":0.00154,"epssPercentile":0.0491,"vendor":"Red Hat","product":"Red Hat Enterprise Linux 9","affected":["enterprise_linux 10","enterprise_linux 9"],"cvss":6.4,"cvssVector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H","cvssSource":"vendor","cwe":["CWE-763"],"slug":"CVE-2026-63809","body":"## Overview\n\nIn 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63809.json)","depth":"sunlit","depthScore":35,"depthScoreParts":{"impact":35.2,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":208502,"id":"CVE-2026-63809","ts":1790005721068,"field":"cvss","old":null,"new":"6.4"},{"seq":208501,"id":"CVE-2026-63809","ts":1790005721068,"field":"severity","old":"none","new":"medium"}]}