{"id":"CVE-2026-98959","state":"PUBLISHED","title":"btrfs: fix xattr replace when multiple xattrs are packed in the same item","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix xattr replace when multiple xattrs are packed in the same item\n\nIf we have a btrfs_dir_item item that packs multiple xattrs and then we\nreplace the value of one of them (with the setxattr(2) family of syscalls)\nwith another value of a different size, we end up not having a fully\ninitialized btrfs_dir_item, resulting in a corruption that the tree\nchecker will detect at extent buffer writeback time.\n\nThis is because in btrfs_setxattr() when we find a btrfs_dir_item with\nmultiple xattrs (due to the crc32c hash of their name being the same)\nwe delete one of the xattr items (btrfs_dir_item) and then insert a new\none, but the deletion and insertion results in shifting existing data in\nthe leaf and therefore when the new value of a xattr has a different size,\nthe new btrfs_dir_item is placed in a leaf section that was not\ninitialized and we only copy the value's data and set the value's length\nin the new btrfs_dir_item, without setting the name, the name's length,\nthe key (which must be all zeroes for xattrs), flags (BTRFS_FT_XATTR) and\ntransaction ID.\n\nThe following script reproduces the issue:\n\n  $ cat test.sh\n  #!/bin/bash\n\n  DEV=/dev/sdi\n  MNT=/mnt/sdi\n\n  mkfs.btrfs -f $DEV\n  mount $DEV $MNT\n\n  touch $MNT/testfile\n\n  # Add two xattrs that, on btrfs, have the same hash (crc32c) for their\n  # name and therefore are packed into the same btrfs_dir_item.\n  setfattr -n user.foobar -v 123 $MNT/testfile\n  setfattr -n user.WvG1c1Td -v qwerty $MNT/testfile\n\n  # Verify the xattrs are present.\n  echo \"xattrs before:\"\n  getfattr --absolute-names --dump $MNT/testfile\n\n  # Now replace the value of the foobar xattr with a significantly larger\n  # value.\n  setfattr -n user.foobar -v abcdefghijklmnopqrstuvwxyz $MNT/testfile\n\n  # Check the xattrs have the expected values.\n  echo \"xattrs after:\"\n  getfattr --absolute-names --dump $MNT/testfile\n\n  umount $MNT\n\nRunning it:\n\n  $ ./test.sh\n  (...)\n  xattrs before:\n  # file: /mnt/sdi/testfile\n  user.WvG1c1Td=\"qwerty\"\n  user.foobar=\"123\"\n\n  xattrs after:\n  # file: /mnt/sdi/testfile\n  user.WvG1c1Td=\"qwerty\"\n\nSo the \"user.foobar\" xattr is missing and there was a transaction abort\nwhen unmounting the fs with the following traces in dmesg:\n\n  $ dmesg\n  [869800.159271] BTRFS warning (device sdi): access to eb bytenr 30474240 len 16384 out of range start 16015 len 25964\n  [869800.159293] ------------[ cut here ]------------\n  [869800.159296] WARNING: fs/btrfs/extent_io.c:4408 at report_eb_range+0x44/0x60 [btrfs], CPU#8: getfattr/2605179\n  [869800.168961] Modules linked in: btrfs dm_thin_pool (...)\n  [869800.190527] CPU: 8 UID: 0 PID: 2605179 Comm: getfattr Tainted: G        W           7.3.0-rc3-btrfs-next-244+ #1 PREEMPT(full)\n  [869800.193726] Tainted: [W]=WARN\n  [869800.194502] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014\n  [869800.197576] RIP: 0010:report_eb_range+0x44/0x60 [btrfs]\n  [869800.198985] Code: 48 8b 7b 18 (...)\n  [869800.203531] RSP: 0018:ffffce4541937d58 EFLAGS: 00010246\n  [869800.204609] RAX: 0000000000000000 RBX: ffff8dde054b8738 RCX: 0000000000000000\n  [869800.206137] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffc04c92a0\n  [869800.207645] RBP: 0000000000003e8f R08: 0000000000000000 R09: 3fffffffffefffff\n  [869800.226175] R10: ffffce4541937a88 R11: 0000000000000003 R12: 000000000000656c\n  [869800.227594] R13: ffff8dde14be800f R14: 000000000000656c R15: 0000000000000069\n  [869800.229097] FS:  00007f59023bb780(0000) GS:ffff8de5788ed000(0000) knlGS:0000000000000000\n  [869800.231137] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n  [869800.232321] CR2: 0000558dc45e6a78 CR3: 0000000765b16004 CR4: 0000000000370ef0\n  [869800.233783] Call Trace:\n  [869800.234330]  <TASK>\n  [869800.234791]  read_extent_buffer+0x4d/0x100 [btrfs]\n  [869800.235898]  btrfs_listxattr+0x199/0x240 [btrfs]\n  [869800.236912]  vfs_listxattr+0x51/0\n---truncated---","publishedAt":"2026-10-23T12:19:27.679Z","updatedAt":"2026-10-24T14:09:39.735Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"7a53bb4668b319fc6c8a3ce2c21635125c7d2712","versionType":"git"},{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"5877d7138cc4359d26fd7b010eedfd1b3162348f","versionType":"git"},{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"a97114b9b00ed3d05156f3b2ddbf797296260389","versionType":"git"},{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"c1803697a60f22743aa28ad522f805e92d45e3f0","versionType":"git"},{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"858bee1c77857aabcc2327cd32dd8266332de332","versionType":"git"},{"version":"43f2e3615d181a7028ab797114c5960977669b2a","status":"affected","versionType":"git"},{"version":"a873146ce4fb025c0b5c1322af5a6bad042f5363","status":"affected","versionType":"git"},{"version":"02590fd855d1690568b2fa439c942e933221b57a","status":"affected","versionType":"git"},{"version":"55e97f654cbbbef70f9714f0e113604dd931e360","status":"affected","versionType":"git"},{"version":"3.10.83","status":"affected","lessThan":"3.11","versionType":"semver"},{"version":"3.12.45","status":"affected","lessThan":"3.13","versionType":"semver"},{"version":"3.14.47","status":"affected","lessThan":"3.15","versionType":"semver"},{"version":"3.18.19","status":"affected","lessThan":"3.19","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/xattr.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.19","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.113","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/xattr.c"]}],"references":["https://git.kernel.org/stable/c/7a53bb4668b319fc6c8a3ce2c21635125c7d2712","https://git.kernel.org/stable/c/5877d7138cc4359d26fd7b010eedfd1b3162348f","https://git.kernel.org/stable/c/a97114b9b00ed3d05156f3b2ddbf797296260389","https://git.kernel.org/stable/c/c1803697a60f22743aa28ad522f805e92d45e3f0","https://git.kernel.org/stable/c/858bee1c77857aabcc2327cd32dd8266332de332"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98959.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98959","state":"PUBLISHED","datePublished":"2026-10-23T12:19:27.679Z","dateUpdated":"2026-10-24T14:09:39.735Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.382Z"},"containers":{"cna":{"title":"btrfs: fix xattr replace when multiple xattrs are packed in the same item","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix xattr replace when multiple xattrs are packed in the same item\n\nIf we have a btrfs_dir_item item that packs multiple xattrs and then we\nreplace the value of one of them (with the setxattr(2) family of syscalls)\nwith another value of a different size, we end up not having a fully\ninitialized btrfs_dir_item, resulting in a corruption that the tree\nchecker will detect at extent buffer writeback time.\n\nThis is because in btrfs_setxattr() when we find a btrfs_dir_item with\nmultiple xattrs (due to the crc32c hash of their name being the same)\nwe delete one of the xattr items (btrfs_dir_item) and then insert a new\none, but the deletion and insertion results in shifting existing data in\nthe leaf and therefore when the new value of a xattr has a different size,\nthe new btrfs_dir_item is placed in a leaf section that was not\ninitialized and we only copy the value's data and set the value's length\nin the new btrfs_dir_item, without setting the name, the name's length,\nthe key (which must be all zeroes for xattrs), flags (BTRFS_FT_XATTR) and\ntransaction ID.\n\nThe following script reproduces the issue:\n\n  $ cat test.sh\n  #!/bin/bash\n\n  DEV=/dev/sdi\n  MNT=/mnt/sdi\n\n  mkfs.btrfs -f $DEV\n  mount $DEV $MNT\n\n  touch $MNT/testfile\n\n  # Add two xattrs that, on btrfs, have the same hash (crc32c) for their\n  # name and therefore are packed into the same btrfs_dir_item.\n  setfattr -n user.foobar -v 123 $MNT/testfile\n  setfattr -n user.WvG1c1Td -v qwerty $MNT/testfile\n\n  # Verify the xattrs are present.\n  echo \"xattrs before:\"\n  getfattr --absolute-names --dump $MNT/testfile\n\n  # Now replace the value of the foobar xattr with a significantly larger\n  # value.\n  setfattr -n user.foobar -v abcdefghijklmnopqrstuvwxyz $MNT/testfile\n\n  # Check the xattrs have the expected values.\n  echo \"xattrs after:\"\n  getfattr --absolute-names --dump $MNT/testfile\n\n  umount $MNT\n\nRunning it:\n\n  $ ./test.sh\n  (...)\n  xattrs before:\n  # file: /mnt/sdi/testfile\n  user.WvG1c1Td=\"qwerty\"\n  user.foobar=\"123\"\n\n  xattrs after:\n  # file: /mnt/sdi/testfile\n  user.WvG1c1Td=\"qwerty\"\n\nSo the \"user.foobar\" xattr is missing and there was a transaction abort\nwhen unmounting the fs with the following traces in dmesg:\n\n  $ dmesg\n  [869800.159271] BTRFS warning (device sdi): access to eb bytenr 30474240 len 16384 out of range start 16015 len 25964\n  [869800.159293] ------------[ cut here ]------------\n  [869800.159296] WARNING: fs/btrfs/extent_io.c:4408 at report_eb_range+0x44/0x60 [btrfs], CPU#8: getfattr/2605179\n  [869800.168961] Modules linked in: btrfs dm_thin_pool (...)\n  [869800.190527] CPU: 8 UID: 0 PID: 2605179 Comm: getfattr Tainted: G        W           7.3.0-rc3-btrfs-next-244+ #1 PREEMPT(full)\n  [869800.193726] Tainted: [W]=WARN\n  [869800.194502] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014\n  [869800.197576] RIP: 0010:report_eb_range+0x44/0x60 [btrfs]\n  [869800.198985] Code: 48 8b 7b 18 (...)\n  [869800.203531] RSP: 0018:ffffce4541937d58 EFLAGS: 00010246\n  [869800.204609] RAX: 0000000000000000 RBX: ffff8dde054b8738 RCX: 0000000000000000\n  [869800.206137] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffc04c92a0\n  [869800.207645] RBP: 0000000000003e8f R08: 0000000000000000 R09: 3fffffffffefffff\n  [869800.226175] R10: ffffce4541937a88 R11: 0000000000000003 R12: 000000000000656c\n  [869800.227594] R13: ffff8dde14be800f R14: 000000000000656c R15: 0000000000000069\n  [869800.229097] FS:  00007f59023bb780(0000) GS:ffff8de5788ed000(0000) knlGS:0000000000000000\n  [869800.231137] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n  [869800.232321] CR2: 0000558dc45e6a78 CR3: 0000000765b16004 CR4: 0000000000370ef0\n  [869800.233783] Call Trace:\n  [869800.234330]  <TASK>\n  [869800.234791]  read_extent_buffer+0x4d/0x100 [btrfs]\n  [869800.235898]  btrfs_listxattr+0x199/0x240 [btrfs]\n  [869800.236912]  vfs_listxattr+0x51/0\n---truncated---"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"7a53bb4668b319fc6c8a3ce2c21635125c7d2712","versionType":"git"},{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"5877d7138cc4359d26fd7b010eedfd1b3162348f","versionType":"git"},{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"a97114b9b00ed3d05156f3b2ddbf797296260389","versionType":"git"},{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"c1803697a60f22743aa28ad522f805e92d45e3f0","versionType":"git"},{"version":"5f5bc6b1e2d5a6f827bc860ef2dc5b6f365d1339","status":"affected","lessThan":"858bee1c77857aabcc2327cd32dd8266332de332","versionType":"git"},{"version":"43f2e3615d181a7028ab797114c5960977669b2a","status":"affected","versionType":"git"},{"version":"a873146ce4fb025c0b5c1322af5a6bad042f5363","status":"affected","versionType":"git"},{"version":"02590fd855d1690568b2fa439c942e933221b57a","status":"affected","versionType":"git"},{"version":"55e97f654cbbbef70f9714f0e113604dd931e360","status":"affected","versionType":"git"},{"version":"3.10.83","status":"affected","lessThan":"3.11","versionType":"semver"},{"version":"3.12.45","status":"affected","lessThan":"3.13","versionType":"semver"},{"version":"3.14.47","status":"affected","lessThan":"3.15","versionType":"semver"},{"version":"3.18.19","status":"affected","lessThan":"3.19","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/xattr.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.19","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.113","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/btrfs/xattr.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/7a53bb4668b319fc6c8a3ce2c21635125c7d2712"},{"url":"https://git.kernel.org/stable/c/5877d7138cc4359d26fd7b010eedfd1b3162348f"},{"url":"https://git.kernel.org/stable/c/a97114b9b00ed3d05156f3b2ddbf797296260389"},{"url":"https://git.kernel.org/stable/c/c1803697a60f22743aa28ad522f805e92d45e3f0"},{"url":"https://git.kernel.org/stable/c/858bee1c77857aabcc2327cd32dd8266332de332"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - An NFSv4.2 OP_SETXATTR carries each attacker-chosen name and value; nfsd4_decode_xattr_name() prepends user. and nfsd_setxattr() reaches the patched btrfs_setxattr(). One client can send two CRC32C-colliding names followed by a different-sized replacement.\nAC:L - btrfs_name_hash() uses unkeyed CRC32C, permitting deterministic chosen-target, non-NUL collisions; the commit also supplies a fixed collision. Sequential OP_SETXATTR operations fully control packing and replacement without a race or external precondition.\nPR:N - With an AUTH_SYS NFS export, the client merely asserts a uid; nfsd_setxattr() gates the operation with fh_verify(..., NFSD_MAY_WRITE) before __vfs_setxattr_locked(). An unauthenticated client can assert the writable file's owner uid.\nUI:N - The attacker alone can issue PUTFH, the setup and replacement OP_SETXATTR operations, and subsequent GETXATTR operations. No victim must mount attacker-supplied media, open a file, or take another action.\nS:U - The malformed btrfs_dir_item, forged xattrs, leaf disclosure, and transaction abort all affect the same host kernel and filesystem security authority; no VM, IOMMU, or other isolation boundary is crossed.\nC:H - Crafted lengths make btrfs_match_dir_item_name() parse a fake user.* dir_item embedded in the replacement value. Its chosen data_len makes btrfs_getxattr()/read_extent_buffer() copy adjacent leaf contents, including potentially inline data, which NFSv4.2 GETXATTR returns.\nI:H - The same controlled parse can embed a complete security.capability dir_item whose CRC32C matches the item key. btrfs_getxattr() can then supply attacker-chosen V2 capabilities to get_vfs_caps_from_disk(), bypassing CAP_SETFCAP and permitting root code execution.\nA:H - check_dir_item() rejects the malformed entry when btrfs_check_leaf() runs from btree_csum_one_bio(); the resulting writeback failure aborts the transaction and forces the Btrfs filesystem read-only."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-24T14:09:39.735Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.19","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.19","versionEndExcluding":"6.12.113"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.19","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.19","versionEndExcluding":"7.2.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.19","versionEndExcluding":"7.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.10.83"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.12.45"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.14.47"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18.19"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}