{"id":"CVE-2026-97420","state":"PUBLISHED","title":"bpf: NUL-terminate replaced sysctl value","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: NUL-terminate replaced sysctl value\n\nWhen writing to sysctls, proc_sys_call_handler() guarantees that the\nbuffer passed to proc handlers is NUL-terminated. If\nbpf_sysctl_set_new_value() replaces the pending sysctl value, it can\nhand a replacement buffer directly to proc handlers. However, the\nhelper currently copies only buf_len bytes into that buffer without\nappending a NUL terminator, leaving downstream parsers vulnerable to\nout-of-bounds access.\n\nFix this by appending a '\\0' after the replaced value to restore the\nexpected sysctl semantics. Since the helper already rejects buf_len\ngreater than PAGE_SIZE - 1, there is always room for the extra byte.\n\nReproduced in a QEMU x86_64 guest booted with KASAN while exercising\nthe sysctl replacement path with a cgroup/sysctl BPF program. The\nreproducer targets `/proc/sys/net/core/flow_limit_cpu_bitmap`, fills\nthe original user write buffer with non-zero bytes, and overrides the\nsysctl value so the replacement buffer lacks a terminating NUL. Under\nthat setup, the pre-fix kernel reported:\n\n  BUG: KASAN: slab-out-of-bounds in strnchrnul+0x72/0x90\n  Read of size 1 at addr ffff88800de57000 by task repro_patch3/66\n  CPU: 0 UID: 0 PID: 66 Comm: repro_patch3 Not tainted 7.1.0-rc3-00269-g8370ca1f87cc #6 PREEMPT(lazy)\n  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014\n  Call Trace:\n   <TASK>\n   dump_stack_lvl+0x68/0xa0\n   print_report+0xcb/0x5e0\n   ? __virt_addr_valid+0x21d/0x3f0\n   ? strnchrnul+0x72/0x90\n   ? strnchrnul+0x72/0x90\n   kasan_report+0xca/0x100\n   ? strnchrnul+0x72/0x90\n   strnchrnul+0x72/0x90\n   bitmap_parse+0x37/0x2e0\n   flow_limit_cpu_sysctl+0xc6/0x840\n   ? __pfx_flow_limit_cpu_sysctl+0x10/0x10\n   ? __kvmalloc_node_noprof+0x5ba/0x870\n   proc_sys_call_handler+0x31d/0x480\n   ? __pfx_proc_sys_call_handler+0x10/0x10\n   ? selinux_file_permission+0x39f/0x500\n   ? lock_is_held_type+0x9e/0x120\n   vfs_write+0x98e/0x1000\n   ...\n   </TASK>\n  The buggy address is located 0 bytes to the right of\n  allocated 4096-byte region [ffff88800de56000, ffff88800de57000)\nWith this fix applied, rerunning the same sysctl-targeted path yields\nno corresponding KASAN reports.","publishedAt":"2026-09-24T16:03:30.084Z","updatedAt":"2026-10-03T10:58:12.202Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"bfcee1f79aaefa90679ad47690107fb7682724ec","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"c73e4a04eedc677fe91a736d7a5db45100adba5e","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"36d3e9f62dc2beb9299d3bb6f589cb9e07f773fe","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"31377675c3d75603d957c08e338a9ac27e9f6cd5","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"76c14b10f50eb0afcc76e244562fa2d8c661e224","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"3b2814dd842a565fcf9cc370156e1ba9eae16239","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"a66e3b5bacf38d6ab29fa05a9754f7a114485605","versionType":"git"}],"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":"5.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.8","versionType":"semver"},{"version":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","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/bfcee1f79aaefa90679ad47690107fb7682724ec","https://git.kernel.org/stable/c/c73e4a04eedc677fe91a736d7a5db45100adba5e","https://git.kernel.org/stable/c/36d3e9f62dc2beb9299d3bb6f589cb9e07f773fe","https://git.kernel.org/stable/c/31377675c3d75603d957c08e338a9ac27e9f6cd5","https://git.kernel.org/stable/c/76c14b10f50eb0afcc76e244562fa2d8c661e224","https://git.kernel.org/stable/c/3b2814dd842a565fcf9cc370156e1ba9eae16239","https://git.kernel.org/stable/c/a66e3b5bacf38d6ab29fa05a9754f7a114485605"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/97xxx/CVE-2026-97420.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-97420","state":"PUBLISHED","datePublished":"2026-09-24T16:03:30.084Z","dateUpdated":"2026-10-03T10:58:12.202Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-24T14:53:16.868Z"},"containers":{"cna":{"title":"bpf: NUL-terminate replaced sysctl value","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: NUL-terminate replaced sysctl value\n\nWhen writing to sysctls, proc_sys_call_handler() guarantees that the\nbuffer passed to proc handlers is NUL-terminated. If\nbpf_sysctl_set_new_value() replaces the pending sysctl value, it can\nhand a replacement buffer directly to proc handlers. However, the\nhelper currently copies only buf_len bytes into that buffer without\nappending a NUL terminator, leaving downstream parsers vulnerable to\nout-of-bounds access.\n\nFix this by appending a '\\0' after the replaced value to restore the\nexpected sysctl semantics. Since the helper already rejects buf_len\ngreater than PAGE_SIZE - 1, there is always room for the extra byte.\n\nReproduced in a QEMU x86_64 guest booted with KASAN while exercising\nthe sysctl replacement path with a cgroup/sysctl BPF program. The\nreproducer targets `/proc/sys/net/core/flow_limit_cpu_bitmap`, fills\nthe original user write buffer with non-zero bytes, and overrides the\nsysctl value so the replacement buffer lacks a terminating NUL. Under\nthat setup, the pre-fix kernel reported:\n\n  BUG: KASAN: slab-out-of-bounds in strnchrnul+0x72/0x90\n  Read of size 1 at addr ffff88800de57000 by task repro_patch3/66\n  CPU: 0 UID: 0 PID: 66 Comm: repro_patch3 Not tainted 7.1.0-rc3-00269-g8370ca1f87cc #6 PREEMPT(lazy)\n  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014\n  Call Trace:\n   <TASK>\n   dump_stack_lvl+0x68/0xa0\n   print_report+0xcb/0x5e0\n   ? __virt_addr_valid+0x21d/0x3f0\n   ? strnchrnul+0x72/0x90\n   ? strnchrnul+0x72/0x90\n   kasan_report+0xca/0x100\n   ? strnchrnul+0x72/0x90\n   strnchrnul+0x72/0x90\n   bitmap_parse+0x37/0x2e0\n   flow_limit_cpu_sysctl+0xc6/0x840\n   ? __pfx_flow_limit_cpu_sysctl+0x10/0x10\n   ? __kvmalloc_node_noprof+0x5ba/0x870\n   proc_sys_call_handler+0x31d/0x480\n   ? __pfx_proc_sys_call_handler+0x10/0x10\n   ? selinux_file_permission+0x39f/0x500\n   ? lock_is_held_type+0x9e/0x120\n   vfs_write+0x98e/0x1000\n   ...\n   </TASK>\n  The buggy address is located 0 bytes to the right of\n  allocated 4096-byte region [ffff88800de56000, ffff88800de57000)\nWith this fix applied, rerunning the same sysctl-targeted path yields\nno corresponding KASAN reports."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"bfcee1f79aaefa90679ad47690107fb7682724ec","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"c73e4a04eedc677fe91a736d7a5db45100adba5e","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"36d3e9f62dc2beb9299d3bb6f589cb9e07f773fe","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"31377675c3d75603d957c08e338a9ac27e9f6cd5","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"76c14b10f50eb0afcc76e244562fa2d8c661e224","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"3b2814dd842a565fcf9cc370156e1ba9eae16239","versionType":"git"},{"version":"32927393dc1ccd60fb2bdc05b9e8e88753761469","status":"affected","lessThan":"a66e3b5bacf38d6ab29fa05a9754f7a114485605","versionType":"git"}],"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":"5.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.8","versionType":"semver"},{"version":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","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/bfcee1f79aaefa90679ad47690107fb7682724ec"},{"url":"https://git.kernel.org/stable/c/c73e4a04eedc677fe91a736d7a5db45100adba5e"},{"url":"https://git.kernel.org/stable/c/36d3e9f62dc2beb9299d3bb6f589cb9e07f773fe"},{"url":"https://git.kernel.org/stable/c/31377675c3d75603d957c08e338a9ac27e9f6cd5"},{"url":"https://git.kernel.org/stable/c/76c14b10f50eb0afcc76e244562fa2d8c661e224"},{"url":"https://git.kernel.org/stable/c/3b2814dd842a565fcf9cc370156e1ba9eae16239"},{"url":"https://git.kernel.org/stable/c/a66e3b5bacf38d6ab29fa05a9754f7a114485605"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-03T10:58:12.202Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.8","versionEndExcluding":"5.10.271"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.8","versionEndExcluding":"5.15.222"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.8","versionEndExcluding":"6.1.189"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.8","versionEndExcluding":"6.6.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.8","versionEndExcluding":"6.12.111"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.8","versionEndExcluding":"6.18.53"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.8","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}