Linux: Use After Free
CVE-2023-53187 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 6297644db23f77c02ae7961cc542d162629ae2c4, 7569c4294ba6ff9f194635b14876198f8a687c4a, 0657b20c5a76c938612f8409735a8830d257866e as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.16% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 6297644db23f77c02ae7961cc542d162629ae2c4 or 7569c4294ba6ff9f194635b14876198f8a687c4a or 0657b20c5a76c938612f8409735a8830d257866e or 5.16, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.16 or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 01eca70ef8cf499d0cb6d1bbd691558e7792cf17 up to, but not including, 6297644db23f77c02ae7961cc542d162629ae2c4; 5d19abcffd8404078dfa7d7118cec357b5e7bc58 up to, but not including, 7569c4294ba6ff9f194635b14876198f8a687c4a; a9f189716cf15913c453299d72f69c51a9b0f86b up to, but not including, 0657b20c5a76c938612f8409735a8830d257866e; edf3b5aadb2515c808200b904baa5b70a727f0ac; 5.15.128 up to, but not including, 5.16 | 6297644db23f77c02ae7961cc542d162629ae2c4, 7569c4294ba6ff9f194635b14876198f8a687c4a, 0657b20c5a76c938612f8409735a8830d257866e, 5.16 |
| Linux | Linux Kernel | 5.15.128 up to, but not including, 5.16; 6.5 | 5.16 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: btrfs: fix use-after-free of new block group that became unused If a task creates a new block group and that block group becomes unused before we finish its creation, at btrfs_create_pending_block_groups(), then when btrfs_mark_bg_unused() is called against the block group, we assume that the block group is currently in the list of block groups to reclaim, and we move it out of the list of new block groups and into the list of unused block groups. This has two consequences: 1) We move it out of the list of new block groups associated to the current transaction. So the block group creation is not finished and if we attempt to delete the bg because it's unused, we will not find the block group item in the extent tree (or the new block group tree), its device extent items in the device tree etc, resulting in the deletion to fail due to the missing items; 2) We don't increment the reference count on the block group when we move it to the list of unused block groups, because we assumed the block group was on the list of block groups to reclaim, and in that case it already has the correct reference count. However the block group was on the list of new block groups, in which case no extra reference was taken because it's local to the current task. This later results in doing an extra reference count decrement when removing the block group from the unused list, eventually leading the reference count to 0. This second case was caught when running generic/297 from fstests, which produced the following assertion failure and stack trace: [589.559] assertion failed: refcount_read(&block_group->refs) == 1, in fs/btrfs/block-group.c:4299 [589.559] ------------[ cut here ]------------ [589.559] kernel BUG at fs/btrfs/block-group.c:4299! [589.560] invalid opcode: 0000 [#1] PREEMPT SMP PTI [589.560] CPU: 8 PID: 2819134 Comm: umount Tainted: G W 6.4.0-rc6-btrfs-next-134+ #1 [589.560] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014 [589.560] RIP: 0010:btrfs_free_block_groups+0x449/0x4a0 [btrfs] [589.561] Code: 68 62 da c0 (...) [589.561] RSP: 0018:ffffa55a8c3b3d98 EFLAGS: 00010246 [589.561] RAX: 0000000000000058 RBX: ffff8f030d7f2000 RCX: 0000000000000000 [589.562] RDX: 0000000000000000 RSI: ffffffff953f0878 RDI: 00000000ffffffff [589.562] RBP: ffff8f030d7f2088 R08: 0000000000000000 R09: ffffa55a8c3b3c50 [589.562] R10: 0000000000000001 R11: 0000000000000001 R12: ffff8f05850b4c00 [589.562] R13: ffff8f030d7f2090 R14: ffff8f05850b4cd8 R15: dead000000000100 [589.563] FS: 00007f497fd2e840(0000) GS:ffff8f09dfc00000(0000) knlGS:0000000000000000 [589.563] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [589.563] CR2: 00007f497ff8ec10 CR3: 0000000271472006 CR4: 0000000000370ee0 [589.563] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [589.564] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [589.564] Call Trace: [589.564] <TASK> [589.565] ? __die_body+0x1b/0x60 [589.565] ? die+0x39/0x60 [589.565] ? do_trap+0xeb/0x110 [589.565] ? btrfs_free_block_groups+0x449/0x4a0 [btrfs] [589.566] ? do_error_trap+0x6a/0x90 [589.566] ? btrfs_free_block_groups+0x449/0x4a0 [btrfs] [589.566] ? exc_invalid_op+0x4e/0x70 [589.566] ? btrfs_free_block_groups+0x449/0x4a0 [btrfs] [589.567] ? asm_exc_invalid_op+0x16/0x20 [589.567] ? btrfs_free_block_groups+0x449/0x4a0 [btrfs] [589.567] ? btrfs_free_block_groups+0x449/0x4a0 [btrfs] [589.567] close_ctree+0x35d/0x560 [btrfs] [589.568] ? fsnotify_sb_delete+0x13e/0x1d0 [589.568] ? dispose_list+0x3a/0x50 [589.568] ? evict_inodes+0x151/0x1a0 [589.568] generic_shutdown_super+0x73/0x1a0 [589.569] kill_anon_super+0x14/0x30 [589.569] btrfs_kill_super+0x12/0x20 [btrfs] [589.569] deactivate_locked ---truncated---
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
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