356 lines
19 KiB
JSON
356 lines
19 KiB
JSON
{
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"cveId": "CVE-2021-46936",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2024-02-25T13:45:52.720Z",
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"datePublished": "2024-02-27T09:44:02.758Z",
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"dateUpdated": "2026-08-05T08:45:10.624Z"
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"value": "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: 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"
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 7.8,
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},
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{
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"lang": "en",
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"value": "AV:L - The bug is triggered by destroying a network namespace while TCP TIME_WAIT timers remain armed, which requires local syscalls (clone/unshare, socket connect/close); a remote packet alone cannot tear down the netns or hit this teardown ordering.\nAC:L - An attacker fully controls both sides—creating TIME_WAIT sockets (including short-timeout tw_kill paths) and destroying the netns—so the race between ipv4_mib_exit_net freeing stats and tcp_sk_exit_batch purging timers is attacker-driven and has been reproduced in the wild and by syzkaller.\nPR:L - An unprivileged process can create a user+net namespace (CLONE_NEWUSER|CLONE_NEWNET), open loopback TCP connections that enter TIME_WAIT, and exit the netns; CAP_SYS_ADMIN inside the user namespace is sufficient and does not require host root.\nUI:N - Exploitation requires no victim action; the attacker creates the sockets and destroys the namespace themselves.\nS:U - Impact is confined to the host kernel’s networking subsystem authority; this is a standard kernel UAF/privilege-escalation class bug, not a VM/IOMMU/sandbox boundary escape.\nC:H - This is a use-after-free on net->mib.net_statistics in tw_timer_handler; UAF of freed kernel heap/percpu memory can be leveraged for information disclosure once the object is reused.\nI:H - tw_timer_handler performs __NET_INC_STATS writes into the already-freed percpu MIB, yielding a memory-corruption write primitive that can be escalated via heap reuse to integrity compromise or code execution.\nA:H - The vulnerability causes a real-world kernel page-fault panic in softirq context (tw_timer_handler), so availability impact is a full kernel oops/panic."
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