{"id":"CVE-2026-72379","title":"fs: refuse O_TMPFILE creation with an unmapped fsuid or fsgid","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs: refuse O_TMPFILE creation with an unmapped fsuid or fsgid\n\nvfs_tmpfile() never checked that the caller's fsuid and fsgid map into\nthe filesystem.  On an idmapped mo…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < 74365c6e367725728d5ce36d38ca116c9f77a254","Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < bac8fb0d60254846f3b56957435dcd870ae12948","Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < 503d0568a525b168d9aa5ca046ec72fc5477df84","Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < a2038514e69371eb493083a6a897ed20fcbb8acb","Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < 47e434da476b5a8bcd1e6e52ab03c5ee7764ee78","Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < 539dce1144651f7976fa418e618b0b574bf15eeb","Linux 5.13"],"published":"2026-08-15","updated":"2026-10-30","sourceUpdated":"2026-10-30T12:29:11.407Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-72379","references":[{"url":"https://git.kernel.org/stable/c/74365c6e367725728d5ce36d38ca116c9f77a254"},{"url":"https://git.kernel.org/stable/c/bac8fb0d60254846f3b56957435dcd870ae12948"},{"url":"https://git.kernel.org/stable/c/503d0568a525b168d9aa5ca046ec72fc5477df84"},{"url":"https://git.kernel.org/stable/c/a2038514e69371eb493083a6a897ed20fcbb8acb"},{"url":"https://git.kernel.org/stable/c/47e434da476b5a8bcd1e6e52ab03c5ee7764ee78"},{"url":"https://git.kernel.org/stable/c/539dce1144651f7976fa418e618b0b574bf15eeb"}],"tags":["cve.org"],"epss":0.00215,"epssPercentile":0.1196,"ingestedAt":"2026-11-05T15:02:32.510Z","slug":"CVE-2026-72379","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nfs: refuse O_TMPFILE creation with an unmapped fsuid or fsgid\n\nvfs_tmpfile() never checked that the caller's fsuid and fsgid map into\nthe filesystem.  On an idmapped mount whose idmapping does not cover the\ncaller's fs{u,g}id, the ->tmpfile() instance initializes the new inode\nthrough inode_init_owner(), where mapped_fsuid()/mapped_fsgid() return\nINVALID_UID/INVALID_GID, and the tmpfile ends up owned by (uid_t)-1.\n\nEvery other creation path already refuses this: may_o_create() (O_CREAT)\nand may_create_dentry() (mkdir, mknod, symlink, link) bail out with\n-EOVERFLOW via fsuidgid_has_mapping() precisely so that an object cannot\nbe created with an owner the filesystem cannot represent.  An O_TMPFILE\nis no exception: it is created I_LINKABLE and linkat(2) can splice it\ninto the namespace afterwards, so the same guarantee must hold.\n\nAdd the missing fsuidgid_has_mapping() check to vfs_tmpfile().  On a\nnon-idmapped mount the caller's fs{u,g}id always map in the superblock's\nuser namespace, so this is a no-op there and only takes effect on an\nidmapped mount that does not map the caller.  It applies to every\nfilesystem that sets FS_ALLOW_IDMAP and implements ->tmpfile() (tmpfs,\next4, btrfs, xfs, f2fs, ...), and to overlayfs, whose upper-layer\ntmpfile creation funnels through vfs_tmpfile() via backing_tmpfile_open().\n\n## Affected\n\n- `Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < 74365c6e367725728d5ce36d38ca116c9f77a254`\n- `Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < bac8fb0d60254846f3b56957435dcd870ae12948`\n- `Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < 503d0568a525b168d9aa5ca046ec72fc5477df84`\n- `Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < a2038514e69371eb493083a6a897ed20fcbb8acb`\n- `Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < 47e434da476b5a8bcd1e6e52ab03c5ee7764ee78`\n- `Linux >= 8e5389132ab429604c1a2459b52f0c849a71cc61 < 539dce1144651f7976fa418e618b0b574bf15eeb`\n- `Linux 5.13`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}