{"cve":"CVE-2021-47451","nvd":{"published":"2024-05-22T07:15:10.220","modified":"2026-08-04T10:17:04.087","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: xt_IDLETIMER: fix panic that occurs when timer_type has garbage value\n\nCurrently, when the rule related to IDLETIMER is added, idletimer_tg timer\nstructure is initialized by kmalloc on executing idletimer_tg_create\nfunction. However, in this process timer->timer_type is not defined to\na specific value. Thus, timer->timer_type has garbage value and it occurs\nkernel panic. So, this commit fixes the panic by initializing\ntimer->timer_type using kzalloc instead of kmalloc.\n\nTest commands:\n    # iptables -A OUTPUT -j IDLETIMER --timeout 1 --label test\n    $ cat /sys/class/xt_idletimer/timers/test\n      Killed\n\nSplat looks like:\n    BUG: KASAN: user-memory-access in alarm_expires_remaining+0x49/0x70\n    Read of size 8 at addr 0000002e8c7bc4c8 by task cat/917\n    CPU: 12 PID: 917 Comm: cat Not tainted 5.14.0+ #3 79940a339f71eb14fc81aee1757a20d5bf13eb0e\n    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014\n    Call Trace:\n     dump_stack_lvl+0x6e/0x9c\n     kasan_report.cold+0x112/0x117\n     ? alarm_expires_remaining+0x49/0x70\n     __asan_load8+0x86/0xb0\n     alarm_expires_remaining+0x49/0x70\n     idletimer_tg_show+0xe5/0x19b [xt_IDLETIMER 11219304af9316a21bee5ba9d58f76a6b9bccc6d]\n     dev_attr_show+0x3c/0x60\n     sysfs_kf_seq_show+0x11d/0x1f0\n     ? device_remove_bin_file+0x20/0x20\n     kernfs_seq_show+0xa4/0xb0\n     seq_read_iter+0x29c/0x750\n     kernfs_fop_read_iter+0x25a/0x2c0\n     ? __fsnotify_parent+0x3d1/0x570\n     ? iov_iter_init+0x70/0x90\n     new_sync_read+0x2a7/0x3d0\n     ? __x64_sys_llseek+0x230/0x230\n     ? rw_verify_area+0x81/0x150\n     vfs_read+0x17b/0x240\n     ksys_read+0xd9/0x180\n     ? vfs_write+0x460/0x460\n     ? do_syscall_64+0x16/0xc0\n     ? lockdep_hardirqs_on+0x79/0x120\n     __x64_sys_read+0x43/0x50\n     do_syscall_64+0x3b/0xc0\n     entry_SYSCALL_64_after_hwframe+0x44/0xae\n    RIP: 0033:0x7f0cdc819142\n    Code: c0 e9 c2 fe ff ff 50 48 8d 3d 3a ca 0a 00 e8 f5 19 02 00 0f 1f 44 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24\n    RSP: 002b:00007fff28eee5b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000\n    RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007f0cdc819142\n    RDX: 0000000000020000 RSI: 00007f0cdc032000 RDI: 0000000000000003\n    RBP: 00007f0cdc032000 R08: 00007f0cdc031010 R09: 0000000000000000\n    R10: 0000000000000022 R11: 0000000000000246 R12: 00005607e9ee31f0\n    R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":["CWE-908"],"references":["https://git.kernel.org/stable/c/2a670c323055282c9b72794a491d53cef86bbeaf","https://git.kernel.org/stable/c/902c0b1887522a099aa4e1e6b4b476c2fe5dd13e","https://git.kernel.org/stable/c/cae7cab804c943d723d52724a3aeb07a3f4a2650","https://git.kernel.org/stable/c/2a670c323055282c9b72794a491d53cef86bbeaf","https://git.kernel.org/stable/c/902c0b1887522a099aa4e1e6b4b476c2fe5dd13e"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T21:50:30.954589733+00:00"},"epss":{"cve":"CVE-2021-47451","score":0.00236,"percentile":0.14643,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}