{
  "cveId": "CVE-2021-46936",
  "url": "https://patchblox.com/security/cve/CVE-2021-46936",
  "summary": "CVE-2021-46936 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-46936, released February 27, 2024. It is not reported as exploited. Patch Radar priority: High.",
  "title": "linux: In the Linux kernel, the following vulnerability has been resolved:  net: fix use-after-free in tw_timer_handler  A r...",
  "description": "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\u002B0x20/0x40     Call Trace:      \u003CIRQ\u003E      call_timer_fn\u002B0x2b/0x120      run_timer_softirq\u002B0x1ef/0x450      __do_softirq\u002B0x10d/0x2b8      irq_exit\u002B0xc7/0xd0      smp_apic_timer_interrupt\u002B0x68/0x120      apic_timer_interrupt\u002B0xf/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 (\u0022mib: add net to NET_ADD_STATS_BH\u0022) since the net_statistics is a global variable instead of dynamic allocation and freeing. Actually, commit 61a7e26028b9 (\u0022mib: put net statistics on struct net\u0022) 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",
  "published": "2024-02-27T10:15:08Z",
  "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",
  "epss": 0.00246,
  "epssPercentile": 0.15891,
  "priority": "High",
  "priorityTier": 3,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 12.15 (bookworm)",
      "fixedVersion": "5.15.15-1",
      "fix": "DEBIAN-CVE-2021-46936",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-46936",
      "released": "2024-02-27T10:15:08Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 13.5 (trixie)",
      "fixedVersion": "5.15.15-1",
      "fix": "DEBIAN-CVE-2021-46936",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-46936",
      "released": "2024-02-27T10:15:08Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 14",
      "fixedVersion": "5.15.15-1",
      "fix": "DEBIAN-CVE-2021-46936",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-46936",
      "released": "2024-02-27T10:15:08Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-09T07:25:28Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}