Linux KernelOperating system · Linux

CVE-2024-56581

HIGH · 7.8 CVSS v3.1 Published 2024-12-27

Fix available

A fix is available. Upgrade to 5.4.287 / 5.10.231 or later.

See remediation →

80/100

Remediation priority · High

Zero-click Patch available

Official description

NVD · unedited

In the Linux kernel, the following vulnerability has been resolved: btrfs: ref-verify: fix use-after-free after invalid ref action At btrfs_ref_tree_mod() after we successfully inserted the new ref entry (local variable 'ref') into the respective block entry's rbtree (local variable 'be'), if we find an unexpected action of BTRFS_DROP_DELAYED_REF, we error out and free the ref entry without removing it from the block entry's rbtree. Then in the error path of btrfs_ref_tree_mod() we call btrfs_free_ref_cache(), which iterates over all block entries and then calls free_block_entry() for each one, and there we will trigger a use-after-free when we are called against the block entry to which we added the freed ref entry to its rbtree, since the rbtree still points to the block entry, as we didn't remove it from the rbtree before freeing it in the error path at btrfs_ref_tree_mod(). Fix this by removing the new ref entry from the rbtree before freeing it. Syzbot report this with the following stack traces: BTRFS error (device loop0 state EA): Ref action 2, root 5, ref_root 0, parent 8564736, owner 0, offset 0, num_refs 18446744073709551615 __btrfs_mod_ref+0x7dd/0xac0 fs/btrfs/extent-tree.c:2523 update_ref_for_cow+0x9cd/0x11f0 fs/btrfs/ctree.c:512 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_insert_empty_items+0x9c/0x1a0 fs/btrfs/ctree.c:4314 btrfs_insert_empty_item fs/btrfs/ctree.h:669 [inline] btrfs_insert_orphan_item+0x1f1/0x320 fs/btrfs/orphan.c:23 btrfs_orphan_add+0x6d/0x1a0 fs/btrfs/inode.c:3482 btrfs_unlink+0x267/0x350 fs/btrfs/inode.c:4293 vfs_unlink+0x365/0x650 fs/namei.c:4469 do_unlinkat+0x4ae/0x830 fs/namei.c:4533 __do_sys_unlinkat fs/namei.c:4576 [inline] __se_sys_unlinkat fs/namei.c:4569 [inline] __x64_sys_unlinkat+0xcc/0xf0 fs/namei.c:4569 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f BTRFS error (device loop0 state EA): Ref action 1, root 5, ref_root 5, parent 0, owner 260, offset 0, num_refs 1 __btrfs_mod_ref+0x76b/0xac0 fs/btrfs/extent-tree.c:2521 update_ref_for_cow+0x96a/0x11f0 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_lookup_inode+0xdc/0x480 fs/btrfs/inode-item.c:411 __btrfs_update_delayed_inode+0x1e7/0xb90 fs/btrfs/delayed-inode.c:1030 btrfs_update_delayed_inode fs/btrfs/delayed-inode.c:1114 [inline] __btrfs_commit_inode_delayed_items+0x2318/0x24a0 fs/btrfs/delayed-inode.c:1137 __btrfs_run_delayed_items+0x213/0x490 fs/btrfs/delayed-inode.c:1171 btrfs_commit_transaction+0x8a8/0x3740 fs/btrfs/transaction.c:2313 prepare_to_relocate+0x3c4/0x4c0 fs/btrfs/relocation.c:3586 relocate_block_group+0x16c/0xd40 fs/btrfs/relocation.c:3611 btrfs_relocate_block_group+0x77d/0xd90 fs/btrfs/relocation.c:4081 btrfs_relocate_chunk+0x12c/0x3b0 fs/btrfs/volumes.c:3377 __btrfs_balance+0x1b0f/0x26b0 fs/btrfs/volumes.c:4161 btrfs_balance+0xbdc/0x10c0 fs/btrfs/volumes.c:4538 BTRFS error (device loop0 state EA): Ref action 2, root 5, ref_root 0, parent 8564736, owner 0, offset 0, num_refs 18446744073709551615 __btrfs_mod_ref+0x7dd/0xac0 fs/btrfs/extent-tree.c:2523 update_ref_for_cow+0x9cd/0x11f0 fs/btrfs/ctree.c:512 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_lookup_inode+0xdc/0x480 fs/btrfs/inode-item.c:411 __btrfs_update_delayed_inode+0x1e7/0xb90 fs/btrfs/delayed-inode.c:1030 btrfs_update_delayed_i ---truncated---

Technical summary

dbcve analysis

How this class of weakness works · CWE-416

Memory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.

General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions

NVD · CPE data

Linux KernelOperating system

Affected:>= 4.15, < 5.4.287>= 5.5, < 5.10.231>= 5.11, < 5.15.174>= 5.16, < 6.1.120>= 6.2, < 6.6.64>= 6.7, < 6.12.4= 6.13

CVSS breakdown

From the vector

Attack vector: Local
Complexity: Low
Privileges: Low
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Remediation

dbcve · scoped

Upgrade available Upgrade to 5.4.287 / 5.10.231 / 5.15.174 or later

Fixed in 5.4.2875.10.2315.15.174

Vendor patch git.kernel.org →

Recommended fix High confidence

Upgrade to kernel version 5.4.287, 5.10.231, 5.15.174, or 6.1.120 (or later) depending on your current branch

Identify the currently running Linux kernel version using `uname -r`
Determine which version branch your kernel is based on (e.g., 5.4.x, 5.10.x, 5.15.x, 6.1.x)
Upgrade to the fixed version for your branch: for 4.15-5.4.x upgrade to >= 5.4.287; for 5.5-5.10.x upgrade to >= 5.10.231; for 5.11-5.15.x upgrade to >= 5.15.174; for 5.16-6.1.x upgrade to >= 6.1.120
Use your distribution's package manager to install the updated kernel package (e.g., `apt-get update && apt-get install linux-image-<version>`, `yum update kernel`, or `dnf update kernel`)
Reboot the system to load the fixed kernel
Verify the new kernel version is running with `uname -r`

Caveat Kernel upgrades may require rebooting the system and could have compatibility implications with existing software; test in a staging environment before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

Scan for this in your stack

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References

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2024-56581 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2024-56581?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here

Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
No spam, self-promotion, credentials, or personal data

At a glance

A fix existsUpgrade to 5.4.287 / 5.10.231 or later

Severity 7.8 High

Exploit likelihood EPSS, next 30 days 0.2%

Affects: Linux Kernel

Remediation

A high-priority fix

Get a fix

Estimated effortfrom ~18 hrs

ComplexityComplex

Typical engagementfrom $3,200

What a fix involves

We scope it with you and confirm a fixed quote
A specialist builds a reviewed fix
You deploy it to staging first
Optional re-test once it’s live

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2024-56581 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

Affected products & versions

CVSS breakdown

Remediation

References