CVE-2023-53187 btrfs: fix use-after-free of new block group that became unused

What is CVE-2023-53187?

CVE-2023-53187 is a high-severity use after free vulnerability in Linux kernel, published on 15 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.

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---

Weakness: CWE-416

Which versions are affected by CVE-2023-53187?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2023-53187?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2023-53187 being exploited?

There is no known exploitation of CVE-2023-53187 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-71165, DEBIAN-CVE-2023-53187, GHSA-4xcf-q92v-qp8c, ROOT-OS-UBUNTU-2204-CVE-2023-53187, UBUNTU-CVE-2023-53187.