#CVE-2026-99180

NVD の情報

In the Linux kernel, the following vulnerability has been resolved: unicode: free the map after a grace period generic_ci_d_hash() and generic_ci_d_compare() read sb->s_encoding and dereference the unicode map while a pathwalk in rcu mode holds nothing but rcu_read_lock(). The filesystems that use them, ext4, f2fs and tmpfs, drop the map with utf8_unload() from ->put_super(), which runs when the last reference to the mount goes away. A lookup that is still inside such a filesystem at that point reads a freed map. With a pathwalk held up in utf8_casefold_hash() while the last reference to a casefolded tmpfs goes away: BUG: KASAN: slab-use-after-free in utf8nlookup+0x74c/0x950 Read of size 8 at addr ff110001030fe658 by task walker/98 Call Trace: <TASK> utf8nlookup+0x74c/0x950 utf8byte+0x160/0x1560 utf8_casefold_hash+0x167/0x230 generic_ci_d_hash+0xdd/0x1c0 link_path_walk+0x11ad/0x1d30 path_lookupat+0x63/0xb00 filename_lookup+0x1f1/0x5b0 vfs_statx+0xd7/0x3b0 [...] Allocated by task 94: __kmalloc_cache_noprof+0x249/0x560 utf8_load+0x4e/0x570 shmem_parse_opt_casefold.isra.0+0x92/0x270 [...] Freed by task 97: kfree+0x1db/0x5b0 shmem_put_super+0x72/0x170 generic_shutdown_super+0x14c/0x530 kill_anon_super+0x3a/0x60 deactivate_locked_super+0x9c/0xf0 cleanup_mnt+0x9f/0x130 So far that has been hard to hit. umount(2) waits for a grace period in namespace_unlock() before it drops the mount, so only a mount whose last reference goes away elsewhere, like the close of a file or a chdir out of a lazily unmounted directory, can race a walker. So it is reachable. Delay the free until a grace period has passed. The map and the data table it holds a reference to then outlive any pathwalk that found the superblock before the mount went away. The reference on the data table module is dropped from the rcu callback as well. utf8-core is built in whenever CONFIG_UNICODE is set, so there is no module exit that would have to wait for the callbacks. Overlayfs points the s_encoding of an overlay at the map of its first layer without taking a reference of its own. That stays correct. The layer is held by the overlay, so its map is dropped only after the overlay is gone.

公開日

2026-10-28

最終更新（NVD）

2026-10-31

NVD の状態

Received

深刻度（CVSS）

• 7.8 HighCVSS 3.1／副／評価：416baaa9-dc9f-4396-8d5f-8c081fb06d67CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

悪用の状況

CISA KEV には掲載されていません（掲載されていないことは、悪用されていないことの証明ではありません）。

EPSS：今後30日に悪用される推定確率 0.18%（全体の上位 92.1%、評価日 2026-10-31）

解消方法

• 解消方法の情報なし

「NVD の条件から推定」は、NVD が影響ありとする版の上限から読み取ったもので、修正版とは限りません。「解消方法の情報なし」は、修正が無いという意味ではありません。必ずベンダーの公告で確認してください。

編集部の記載（レポート掲載時）

レポートの編集部がベンダー公告などから転記した内容です。検証済みの値ではないため、必ず出典で確認してください。

参照（NVD）

• https://git.kernel.org/stable/c/092e14e1479a39157ca01668d43e4649793f39ed
• https://git.kernel.org/stable/c/2b54d3c971a1e5df3c9b0bcc10311ae6c29e79d8
• https://git.kernel.org/stable/c/5d7687b0b71601cc32f1bfd62f56cf5eea3e5a07
• https://git.kernel.org/stable/c/6472455f2b015cad43adb790cb63fe1d3cff2f57
• https://git.kernel.org/stable/c/6560c3d9a6925e3747d9ad8463e16010c31ba715
• https://git.kernel.org/stable/c/69a0d6b31d05e856c7335509222f25321e3c69ca
• https://git.kernel.org/stable/c/a96c5299bd7305eb984377681eb3222a57376405
• https://git.kernel.org/stable/c/f96c2731a105d6663c606388f5dc21781e00ade5