CVE-2023-53618 btrfs: reject invalid reloc tree root keys with stack dump

What is CVE-2023-53618?

CVE-2023-53618 is a medium-severity denial of service vulnerability in Linux kernel, published on 7 Oct 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: reject invalid reloc tree root keys with stack dump

[BUG] Syzbot reported a crash that an ASSERT() got triggered inside prepare_to_merge().

That ASSERT() makes sure the reloc tree is properly pointed back by its subvolume tree.

[CAUSE] After more debugging output, it turns out we had an invalid reloc tree:

BTRFS error (device loop1): reloc tree mismatch, root 8 has no reloc root, expect reloc root key (-8, 132, 8) gen 17

Note the above root key is (TREE_RELOC_OBJECTID, ROOT_ITEM, QUOTA_TREE_OBJECTID), meaning it's a reloc tree for quota tree.

But reloc trees can only exist for subvolumes, as for non-subvolume trees, we just COW the involved tree block, no need to create a reloc tree since those tree blocks won't be shared with other trees.

Only subvolumes tree can share tree blocks with other trees (thus they have BTRFS_ROOT_SHAREABLE flag).

Thus this new debug output proves my previous assumption that corrupted on-disk data can trigger that ASSERT().

[FIX] Besides the dedicated fix and the graceful exit, also let tree-checker to check such root keys, to make sure reloc trees can only exist for subvolumes.

Which versions are affected by CVE-2023-53618?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2023-53618?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2023-53618 being exploited?

There is no known exploitation of CVE-2023-53618 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 BELL-CVE-2023-53618, DEBIAN-CVE-2023-53618, GHSA-2244-8r8j-955v, ROOT-OS-DEBIAN-11-CVE-2023-53618, UBUNTU-CVE-2023-53618.