{
  "cveId": "CVE-2021-47656",
  "url": "https://patchblox.com/security/cve/CVE-2021-47656",
  "summary": "CVE-2021-47656 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47656, released February 26, 2025. It is not reported as exploited. Patch Radar priority: High.",
  "title": "linux: In the Linux kernel, the following vulnerability has been resolved:  jffs2: fix use-after-free in jffs2_clear_xattr_s...",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  jffs2: fix use-after-free in jffs2_clear_xattr_subsystem  When we mount a jffs2 image, assume that the first few blocks of the image are normal and contain at least one xattr-related inode, but the next block is abnormal. As a result, an error is returned in jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then called in jffs2_build_filesystem() and then again in jffs2_do_fill_super().  Finally we can observe the following report:  ==================================================================  BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem\u002B0x95/0x6ac  Read of size 8 at addr ffff8881243384e0 by task mount/719   Call Trace:   dump_stack\u002B0x115/0x16b   jffs2_clear_xattr_subsystem\u002B0x95/0x6ac   jffs2_do_fill_super\u002B0x84f/0xc30   jffs2_fill_super\u002B0x2ea/0x4c0   mtd_get_sb\u002B0x254/0x400   mtd_get_sb_by_nr\u002B0x4f/0xd0   get_tree_mtd\u002B0x498/0x840   jffs2_get_tree\u002B0x25/0x30   vfs_get_tree\u002B0x8d/0x2e0   path_mount\u002B0x50f/0x1e50   do_mount\u002B0x107/0x130   __se_sys_mount\u002B0x1c5/0x2f0   __x64_sys_mount\u002B0xc7/0x160   do_syscall_64\u002B0x45/0x70   entry_SYSCALL_64_after_hwframe\u002B0x44/0xa9   Allocated by task 719:   kasan_save_stack\u002B0x23/0x60   __kasan_kmalloc.constprop.0\u002B0x10b/0x120   kasan_slab_alloc\u002B0x12/0x20   kmem_cache_alloc\u002B0x1c0/0x870   jffs2_alloc_xattr_ref\u002B0x2f/0xa0   jffs2_scan_medium.cold\u002B0x3713/0x4794   jffs2_do_mount_fs.cold\u002B0xa7/0x2253   jffs2_do_fill_super\u002B0x383/0xc30   jffs2_fill_super\u002B0x2ea/0x4c0  [...]   Freed by task 719:   kmem_cache_free\u002B0xcc/0x7b0   jffs2_free_xattr_ref\u002B0x78/0x98   jffs2_clear_xattr_subsystem\u002B0xa1/0x6ac   jffs2_do_mount_fs.cold\u002B0x5e6/0x2253   jffs2_do_fill_super\u002B0x383/0xc30   jffs2_fill_super\u002B0x2ea/0x4c0  [...]   The buggy address belongs to the object at ffff8881243384b8   which belongs to the cache jffs2_xattr_ref of size 48  The buggy address is located 40 bytes inside of   48-byte region [ffff8881243384b8, ffff8881243384e8)  [...]  ==================================================================  The triggering of the BUG is shown in the following stack: ----------------------------------------------------------- jffs2_fill_super   jffs2_do_fill_super     jffs2_do_mount_fs       jffs2_build_filesystem         jffs2_scan_medium           jffs2_scan_eraseblock        \u003C--- ERROR         jffs2_clear_xattr_subsystem    \u003C--- free     jffs2_clear_xattr_subsystem        \u003C--- free again -----------------------------------------------------------  An error is returned in jffs2_do_mount_fs(). If the error is returned by jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to be executed. If the error is returned by jffs2_build_filesystem(), the jffs2_clear_xattr_subsystem() also does not need to be executed again. So move jffs2_clear_xattr_subsystem() from \u0027out_inohash\u0027 to \u0027out_root\u0027 to fix this UAF problem.",
  "published": "2025-02-26T06:37:07Z",
  "severity": "high",
  "cvss": 7.8,
  "cvssVector": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
  "epss": 0.00258,
  "epssPercentile": 0.17602,
  "priority": "High",
  "priorityTier": 3,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 12.15 (bookworm)",
      "fixedVersion": "5.17.3-1",
      "fix": "DEBIAN-CVE-2021-47656",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-47656",
      "released": "2025-02-26T06:37:07Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 13.5 (trixie)",
      "fixedVersion": "5.17.3-1",
      "fix": "DEBIAN-CVE-2021-47656",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-47656",
      "released": "2025-02-26T06:37:07Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 14",
      "fixedVersion": "5.17.3-1",
      "fix": "DEBIAN-CVE-2021-47656",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-47656",
      "released": "2025-02-26T06:37:07Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T00:53:09Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}