{"id":"DEBIAN-CVE-2021-46936","details":"In the Linux kernel, the following vulnerability has been resolved:  net: fix use-after-free in tw_timer_handler  A real world panic issue was found as follow in Linux 5.4.      BUG: unable to handle page fault for address: ffffde49a863de28     PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0     RIP: 0010:tw_timer_handler+0x20/0x40     Call Trace:      \u003cIRQ\u003e      call_timer_fn+0x2b/0x120      run_timer_softirq+0x1ef/0x450      __do_softirq+0x10d/0x2b8      irq_exit+0xc7/0xd0      smp_apic_timer_interrupt+0x68/0x120      apic_timer_interrupt+0xf/0x20  This issue was also reported since 2017 in the thread [1], unfortunately, the issue was still can be reproduced after fixing DCCP.  The ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net namespace is destroyed since tcp_sk_ops is registered befrore ipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops in the list of pernet_list. There will be a use-after-free on net-\u003emib.net_statistics in tw_timer_handler after ipv4_mib_exit_net if there are some inflight time-wait timers.  This bug is not introduced by commit f2bf415cfed7 (\"mib: add net to NET_ADD_STATS_BH\") since the net_statistics is a global variable instead of dynamic allocation and freeing. Actually, commit 61a7e26028b9 (\"mib: put net statistics on struct net\") introduces the bug since it put net statistics on struct net and free it when net namespace is destroyed.  Moving init_ipv4_mibs() to the front of tcp_init() to fix this bug and replace pr_crit() with panic() since continuing is meaningless when init_ipv4_mibs() fails.  [1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1","modified":"2026-09-15T09:02:30.541682312Z","published":"2024-02-27T10:15:08.017Z","upstream":["CVE-2021-46936"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2021-46936"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.15.15-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2021-46936.json"}},{"package":{"name":"linux","ecosystem":"Debian:13","purl":"pkg:deb/debian/linux?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.15.15-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2021-46936.json"}},{"package":{"name":"linux","ecosystem":"Debian:14","purl":"pkg:deb/debian/linux?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.15.15-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2021-46936.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}