Linux Kernel up to 6.6.129/6.12.74/6.18.13/6.19.3 ext4_mb_complex_scan_group:2508 race condition

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6.1$0-$5k0.00

Summaryinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 6.6.129/6.12.74/6.18.13/6.19.3. The impacted element is the function ext4_mb_complex_scan_group:2508. The manipulation results in race condition. This vulnerability is identified as CVE-2026-45942. There is not any exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 6.6.129/6.12.74/6.18.13/6.19.3. Affected is the function ext4_mb_complex_scan_group:2508. The manipulation with an unknown input leads to a race condition vulnerability. CWE is classifying the issue as CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: ext4: fix e4b bitmap inconsistency reports A bitmap inconsistency issue was observed during stress tests under mixed huge-page workloads. Ext4 reported multiple e4b bitmap check failures like: ext4_mb_complex_scan_group:2508: group 350, 8179 free clusters as per group info. But got 8192 blocks Analysis and experimentation confirmed that the issue is caused by a race condition between page migration and bitmap modification. Although this timing window is extremely narrow, it is still hit in practice: folio_lock ext4_mb_load_buddy __migrate_folio check ref count folio_mc_copy __filemap_get_folio folio_try_get(folio) ...... mb_mark_used ext4_mb_unload_buddy __folio_migrate_mapping folio_ref_freeze folio_unlock The root cause of this issue is that the fast path of load_buddy only increments the folio's reference count, which is insufficient to prevent concurrent folio migration. We observed that the folio migration process acquires the folio lock. Therefore, we can determine whether to take the fast path in load_buddy by checking the lock status. If the folio is locked, we opt for the slow path (which acquires the lock) to close this concurrency window. Additionally, this change addresses the following issues: When the DOUBLE_CHECK macro is enabled to inspect bitmap-related issues, the following error may be triggered: corruption in group 324 at byte 784(6272): f in copy != ff on disk/prealloc Analysis reveals that this is a false positive. There is a specific race window where the bitmap and the group descriptor become momentarily inconsistent, leading to this error report: ext4_mb_load_buddy ext4_mb_load_buddy __filemap_get_folio(create|lock) folio_lock ext4_mb_init_cache folio_mark_uptodate __filemap_get_folio(no lock) ...... mb_mark_used mb_mark_used_double mb_cmp_bitmaps mb_set_bits(e4b->bd_bitmap) folio_unlock The original logic assumed that since mb_cmp_bitmaps is called when the bitmap is newly loaded from disk, the folio lock would be sufficient to prevent concurrent access. However, this overlooks a specific race condition: if another process attempts to load buddy and finds the folio is already in an uptodate state, it will immediately begin using it without holding folio lock.

The advisory is available at git.kernel.org. This vulnerability is traded as CVE-2026-45942 since 05/13/2026. The exploitability is told to be difficult. Technical details are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 321697 (SUSE SLES16 Security Update : kernel (SUSE-SU-2026:22099-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.6.130, 6.12.75, 6.18.14 or 6.19.4 eliminates this vulnerability. Applying the patch 57e83bfbe1e412ac42daced2086f3c6f9a17bba0/c05033cfc5c7699cd4df8d48cef94d01da755f24/29a07d691d282faf38c33d4b61839b89399110f9/f29709a7a3fc38f5015d850504762cdef0e151f9/bdc56a9c46b2a99c12313122b9352b619a2e719e 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 vulnerability database at Tenable (321697). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.2
VulDB Meta Temp Score: 6.1

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

CNA Base Score: 7.8
CNA Vector (Linux): 🔒

CVSSv2info

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

Exploitinginfo

Class: Race condition
CWE: CWE-362
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 321697
Nessus Name: SUSE SLES16 Security Update : kernel (SUSE-SU-2026:22099-1)

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.6.130/6.12.75/6.18.14/6.19.4
Patch: 57e83bfbe1e412ac42daced2086f3c6f9a17bba0/c05033cfc5c7699cd4df8d48cef94d01da755f24/29a07d691d282faf38c33d4b61839b89399110f9/f29709a7a3fc38f5015d850504762cdef0e151f9/bdc56a9c46b2a99c12313122b9352b619a2e719e

Timelineinfo

05/13/2026 CVE reserved
05/27/2026 +14 days Advisory disclosed
05/27/2026 +0 days VulDB entry created
06/25/2026 +28 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-45942 (🔒)
GCVE (CVE): GCVE-0-2026-45942
GCVE (VulDB): GCVE-100-366186

Entryinfo

Created: 05/27/2026 17:08
Updated: 06/25/2026 01:15
Changes: 05/27/2026 17:08 (58), 06/21/2026 07:48 (2), 06/25/2026 01:15 (11)
Complete: 🔍
Cache ID: 216::103

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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