{
  "cveId": "CVE-2026-63811",
  "url": "https://patchblox.com/security/cve/CVE-2026-63811",
  "summary": "CVE-2026-63811 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-63811, released July 20, 2026. It is not reported as exploited. Patch Radar priority: Routine.",
  "title": "f2fs: read COW data with the original inode during atomic write",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  f2fs: read COW data with the original inode during atomic write  When updating an atomic-write file, f2fs_write_begin() may read the previously written data back from the COW inode: prepare_atomic_write_begin() locates the block in the COW inode and sets use_cow, and the read bio is then built with the COW inode:  \tf2fs_submit_page_read(use_cow ? F2FS_I(inode)-\u003Ecow_inode : inode, \t\t\t      ...);  and f2fs_grab_read_bio() decides whether to schedule fs-layer decryption (STEP_DECRYPT) for the bio based on that inode via fscrypt_inode_uses_fs_layer_crypto().  However, the folio being filled belongs to the original inode (folio-\u003Emapping-\u003Ehost == inode), and the data stored in the COW block was encrypted (or left as plaintext) using the original inode\u0027s context, not the COW inode\u0027s -- see f2fs_encrypt_one_page(), which keys off fio-\u003Epage-\u003Emapping-\u003Ehost.  fscrypt_decrypt_pagecache_blocks() likewise operates on folio-\u003Emapping-\u003Ehost.  The COW inode is created as a tmpfile in the parent directory and inherits its encryption policy from there.  With test_dummy_encryption the newly created COW inode gets the dummy policy and becomes encrypted, while a pre-existing regular file -- created before the policy applied, e.g. already present in the on-disk image -- stays unencrypted.  The read path then sets STEP_DECRYPT based on the encrypted COW inode and calls fscrypt_decrypt_pagecache_blocks() on a folio whose host (the unencrypted original inode) has a NULL -\u003Ei_crypt_info, dereferencing it:    Oops: general protection fault, probably for non-canonical address ...   KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]   RIP: 0010:fscrypt_decrypt_pagecache_blocks\u002B0xa0/0x310   Workqueue: f2fs_post_read_wq f2fs_post_read_work   Call Trace:    fscrypt_decrypt_bio\u002B0x1eb/0x340    f2fs_post_read_work\u002B0xba/0x140    process_one_work\u002B0x91c/0x1a40    worker_thread\u002B0x677/0xe90    kthread\u002B0x2bc/0x3a0  The COW inode is only needed to locate the on-disk block, and that block address is already resolved into @blkaddr by prepare_atomic_write_begin() via __find_data_block(cow_inode, ...); f2fs_submit_page_read() then reads from that physical @blkaddr directly, so the inode argument only selects the post-read crypto context, not which block is fetched.  Reading with @inode therefore returns the same (latest, not-yet-committed) COW data, while making both the fs-layer decryption decision and the inline crypto path use the correct (original inode\u0027s) key.  With the COW inode no longer used at the read site, the use_cow flag has no remaining consumer; drop it from f2fs_write_begin() and prepare_atomic_write_begin().",
  "published": "2026-07-19T12:16:54Z",
  "severity": "Moderate",
  "cvss": 5.5,
  "epss": 0.00135,
  "epssPercentile": 0.02996,
  "priority": "Routine",
  "priorityTier": 4,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "vendorAdvisory": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-63811",
  "fixes": [
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 13.5 (trixie)",
      "fixedVersion": "6.12.115-2",
      "fix": "DEBIAN-CVE-2026-63811",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-63811",
      "released": "2026-07-20T12:58:36Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 14",
      "fixedVersion": "7.1.3-1",
      "fix": "DEBIAN-CVE-2026-63811",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-63811",
      "released": "2026-07-20T12:58:36Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-10T07:50:38Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}