{"id":"CVE-2021-46936","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix use-after-free in tw_timer_handler\n\nA real world panic issue was found as follow in Linux 5.4.\n\n    BUG: unable to handle page fault for address: ffffde49a863d…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix use-after-free in tw_timer_handler\n\nA real world panic issue was found as follow in Linux 5.4.\n\n    BUG: unable to handle page fault for address: ffffde49a863d…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cwe":["CWE-416"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 2.6.27, < 4.4.298","linux_kernel >= 4.5.0, < 4.9.296","linux_kernel >= 4.10.0, < 4.14.261","linux_kernel >= 4.15.0, < 4.19.224","linux_kernel >= 4.20.0, < 5.4.170","linux_kernel >= 5.5.0, < 5.10.90","linux_kernel >= 5.11.0, < 5.15.13"],"patched":["linux_kernel 5.15.13"],"published":"2024-02-27","updated":"2026-08-04","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2021-46936","references":[{"url":"https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69","label":"af854a3a-2127-422b-91ae-364da2661108"}],"tags":["nvd"],"epss":0.00246,"epssPercentile":0.16107,"ingestedAt":"2026-08-04T10:39:38.434Z","slug":"CVE-2021-46936","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix use-after-free in tw_timer_handler\n\nA real world panic issue was found as follow in Linux 5.4.\n\n    BUG: unable to handle page fault for address: ffffde49a863de28\n    PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0\n    RIP: 0010:tw_timer_handler+0x20/0x40\n    Call Trace:\n     <IRQ>\n     call_timer_fn+0x2b/0x120\n     run_timer_softirq+0x1ef/0x450\n     __do_softirq+0x10d/0x2b8\n     irq_exit+0xc7/0xd0\n     smp_apic_timer_interrupt+0x68/0x120\n     apic_timer_interrupt+0xf/0x20\n\nThis issue was also reported since 2017 in the thread [1],\nunfortunately, the issue was still can be reproduced after fixing\nDCCP.\n\nThe ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net\nnamespace is destroyed since tcp_sk_ops is registered befrore\nipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops\nin the list of pernet_list. There will be a use-after-free on\nnet->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net\nif there are some inflight time-wait timers.\n\nThis bug is not introduced by commit f2bf415cfed7 (\"mib: add net to\nNET_ADD_STATS_BH\") since the net_statistics is a global variable\ninstead of dynamic allocation and freeing. Actually, commit\n61a7e26028b9 (\"mib: put net statistics on struct net\") introduces\nthe bug since it put net statistics on struct net and free it when\nnet namespace is destroyed.\n\nMoving init_ipv4_mibs() to the front of tcp_init() to fix this bug\nand replace pr_crit() with panic() since continuing is meaningless\nwhen init_ipv4_mibs() fails.\n\n[1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1\n\n## Affected\n\n- `linux_kernel >= 2.6.27, < 4.4.298`\n- `linux_kernel >= 4.5.0, < 4.9.296`\n- `linux_kernel >= 4.10.0, < 4.14.261`\n- `linux_kernel >= 4.15.0, < 4.19.224`\n- `linux_kernel >= 4.20.0, < 5.4.170`\n- `linux_kernel >= 5.5.0, < 5.10.90`\n- `linux_kernel >= 5.11.0, < 5.15.13`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 5.15.13`","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}