Linux Kernel up to 6.19.10 btrfs_orphan_cleanup privilege escalation

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4.4$0-$5k0.00

Summaryinfo

A vulnerability labeled as problematic has been found in Linux Kernel up to 6.1.167/6.6.130/6.12.79/6.18.20/6.19.10. This affects the function btrfs_orphan_cleanup. The manipulation results in an unknown weakness. This vulnerability is reported as CVE-2026-31519. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.1.167/6.6.130/6.12.79/6.18.20/6.19.10. It has been classified as problematic. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: btrfs: set BTRFS_ROOT_ORPHAN_CLEANUP during subvol create We have recently observed a number of subvolumes with broken dentries. ls-ing the parent dir looks like: drwxrwxrwt 1 root root 16 Jan 23 16:49 . drwxr-xr-x 1 root root 24 Jan 23 16:48 .. d????????? ? ? ? ? ? broken_subvol and similarly stat-ing the file fails. In this state, deleting the subvol fails with ENOENT, but attempting to create a new file or subvol over it errors out with EEXIST and even aborts the fs. Which leaves us a bit stuck. dmesg contains a single notable error message reading: "could not do orphan cleanup -2" 2 is ENOENT and the error comes from the failure handling path of btrfs_orphan_cleanup(), with the stack leading back up to btrfs_lookup(). btrfs_lookup btrfs_lookup_dentry btrfs_orphan_cleanup // prints that message and returns -ENOENT After some detailed inspection of the internal state, it became clear that: - there are no orphan items for the subvol - the subvol is otherwise healthy looking, it is not half-deleted or anything, there is no drop progress, etc. - the subvol was created a while ago and does the meaningful first btrfs_orphan_cleanup() call that sets BTRFS_ROOT_ORPHAN_CLEANUP much later. - after btrfs_orphan_cleanup() fails, btrfs_lookup_dentry() returns -ENOENT, which results in a negative dentry for the subvolume via d_splice_alias(NULL, dentry), leading to the observed behavior. The bug can be mitigated by dropping the dentry cache, at which point we can successfully delete the subvolume if we want. i.e., btrfs_lookup() btrfs_lookup_dentry() if (!sb_rdonly(inode->vfs_inode)->vfs_inode) btrfs_orphan_cleanup(sub_root) test_and_set_bit(BTRFS_ROOT_ORPHAN_CLEANUP) btrfs_search_slot() // finds orphan item for inode N ... prints "could not do orphan cleanup -2" if (inode == ERR_PTR(-ENOENT)) inode = NULL; return d_splice_alias(NULL, dentry) // NEGATIVE DENTRY for valid subvolume btrfs_orphan_cleanup() does test_and_set_bit(BTRFS_ROOT_ORPHAN_CLEANUP) on the root when it runs, so it cannot run more than once on a given root, so something else must run concurrently. However, the obvious routes to deleting an orphan when nlinks goes to 0 should not be able to run without first doing a lookup into the subvolume, which should run btrfs_orphan_cleanup() and set the bit. The final important observation is that create_subvol() calls d_instantiate_new() but does not set BTRFS_ROOT_ORPHAN_CLEANUP, so if the dentry cache gets dropped, the next lookup into the subvolume will make a real call into btrfs_orphan_cleanup() for the first time. This opens up the possibility of concurrently deleting the inode/orphan items but most typical evict() paths will be holding a reference on the parent dentry (child dentry holds parent->d_lockref.count via dget in d_alloc(), released in __dentry_kill()) and prevent the parent from being removed from the dentry cache. The one exception is delayed iputs. Ordered extent creation calls igrab() on the inode. If the file is unlinked and closed while those refs are held, iput() in __dentry_kill() decrements i_count but does not trigger eviction (i_count > 0). The child dentry is freed and the subvol dentry's d_lockref.count drops to 0, making it evictable while the inode is still alive. Since there are two races (the race between writeback and unlink and the race between lookup and delayed iputs), and there are too many moving parts, the following three diagrams show the complete picture. (Only the second and third are races) Phase 1: Create Subvol in dentry cache without BTRFS_ROOT_ORPHAN_CLEANUP set btrfs_mksubvol() lookup_one_len() __lookup_slow() d_alloc_parallel() __d_alloc() // d_lockref.count = 1 create_subvol(dentry) // doesn't touch the bit.. d_instantiate_new(dentry, inode) // dentry in cache with d_lockref.c ---truncated---

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2026-31519 since 03/09/2026. The exploitability is told to be difficult. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 07/26/2026).

The vulnerability scanner Nessus provides a plugin with the ID 316948 (Amazon Linux 2023 : bpftool6.18, kernel6.18, kernel6.18-devel (ALAS2023-2026-1746)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.1.168, 6.6.131, 6.12.80, 6.18.21 or 6.19.11 eliminates this vulnerability. Applying the patch d43da8de0ed376abafbad8a245a1835e8f66cb0f/c57276ced3c3207f42182dfa2f0d8e860357e111/a41a9b8d19a98b45591528c6e54d31cc66271d1e/2ec578e6452138ab76f6c9a9c18711fcd197649f/696683f214495db3cdacab9a713efaaced8660f8/5131fa077f9bb386a1b901bf5b247041f0ec8f80 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (316948) and CERT Bund (WID-SEC-2026-1252). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

  • Google Container-Optimized OS
  • Debian Linux
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • SUSE openSUSE
  • RESF Rocky Linux
  • Open Source Linux Kernel
  • Siemens SIMATIC S7
  • Proxmox Virtual Environment

Productinfo

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Vendor

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Version

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Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.6
VulDB Meta Temp Score: 4.4

VulDB Base Score: 4.6
VulDB Temp Score: 4.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Privilege escalation
CWE: Unknown
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 316948
Nessus Name: Amazon Linux 2023 : bpftool6.18, kernel6.18, kernel6.18-devel (ALAS2023-2026-1746)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.1.168/6.6.131/6.12.80/6.18.21/6.19.11
Patch: d43da8de0ed376abafbad8a245a1835e8f66cb0f/c57276ced3c3207f42182dfa2f0d8e860357e111/a41a9b8d19a98b45591528c6e54d31cc66271d1e/2ec578e6452138ab76f6c9a9c18711fcd197649f/696683f214495db3cdacab9a713efaaced8660f8/5131fa077f9bb386a1b901bf5b247041f0ec8f80

Timelineinfo

03/09/2026 CVE reserved
04/22/2026 +43 days Advisory disclosed
04/22/2026 +0 days VulDB entry created
07/26/2026 +95 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-31519 (🔒)
GCVE (CVE): GCVE-0-2026-31519
GCVE (VulDB): GCVE-100-358872
CERT Bund: WID-SEC-2026-1252 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 04/22/2026 17:05
Updated: 07/26/2026 08:16
Changes: 04/22/2026 17:05 (56), 05/28/2026 00:17 (2), 06/18/2026 08:59 (7), 07/26/2026 08:16 (3)
Complete: 🔍
Cache ID: 216::103

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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