CVE-2026-23403

Description

In the Linux kernel, the following vulnerability has been resolved: apparmor: fix memory leak in verify_header The function sets `*ns = NULL` on every call, leaking the namespace string allocated in previous iterations when multiple profiles are unpacked. This also breaks namespace consistency checking since *ns is always NULL when the comparison is made. Remove the incorrect assignment. The caller (aa_unpack) initializes *ns to NULL once before the loop, which is sufficient.

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 (Specific versions prior to patches in stable branches)

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * PoC for CVE-2026-23403: AppArmor Memory Leak
 * This PoC attempts to trigger the memory leak by repeatedly
 * unpacking profiles. Note: This requires a vulnerable kernel
 * and appropriate privileges to load AppArmor profiles.
 */

#include <stdio.h>
#include <stdlib.h>

// Pseudo-code to demonstrate the loop causing the leak in verify_header
int main() {
    printf("Attempting to trigger CVE-2026-23403...\n");
    printf("Loading profiles to exhaust memory via verify_header leak.\n");

    for (int i = 0; i < 10000; i++) {
        // In a real exploit scenario, replace this with the actual syscall
        // or command to load a profile with a namespace defined.
        // system("apparmor_parser -r profile_with_namespace");
        
        // Simulating the trigger
        alloc_and_leak_namespace();
    }

    return 0;
}

void alloc_and_leak_namespace() {
    // Simulation of the kernel logic where *ns is set to NULL
    // causing the previously allocated memory to leak.
    char *ns = malloc(1024);
    ns = NULL; // The bug: overwriting the pointer without freeing
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-23403
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-23403
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-23403/
[4] VulDB https://vuldb.com/cve/CVE-2026-23403
[5] https://git.kernel.org/stable/c/42fd831abfc15d0643c14688f0522556b347e7e6
[6] https://git.kernel.org/stable/c/4f0889f2df1ab99224a5e1ac4e20437eea5fe38e
[7] https://git.kernel.org/stable/c/663ce34786e759ebcbeb3060685c20bcc886d51a
[8] https://git.kernel.org/stable/c/6b79abcb3c985e153fcf9d395e1d4336081aabc2
[9] https://git.kernel.org/stable/c/786e2c2a87d9c505f33321d1fd23a176aa8ddeb1
[10] https://git.kernel.org/stable/c/9d678eb0fe55c9195d9a253e8c5b82a87b930737
[11] https://git.kernel.org/stable/c/bcf82c0c5a8b383fd2d5d8f3fd880cdcab2ac557
[12] https://git.kernel.org/stable/c/e38c55d9f834e5b848bfed0f5c586aaf45acb825

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-23403", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-01T09:16:15.803", "lastModified": "2026-04-24T18:39:58.850", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\napparmor: fix memory leak in verify_header\n\nThe function sets `*ns = NULL` on every call, leaking the namespace\nstring allocated in previous iterations when multiple profiles are\nunpacked. This also breaks namespace consistency checking since *ns\nis always NULL when the comparison is made.\n\nRemove the incorrect assignment.\nThe caller (aa_unpack) initializes *ns to NULL once before the loop,\nwhich is sufficient."}], "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-401"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.12.1", "versionEndExcluding": "5.10.253", "matchCriteriaId": "0931301A-390F-4D6A-95A4-6D822A49CA04"}, {"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": "6.1.169", "matchCriteriaId": "DBEC0E5D-641C-4E98-A6D9-5799B10CE451"}, {"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": "6.12.77", "matchCriteriaId": "B3D12E00-E42D-4056-B354-BAD4903C03A5"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.18", "matchCriteriaId": "346AD1FB-0CE8-4D9D-8E56-5EB1A4D06199"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.8", "matchCriteriaId": "C65A7D85-C7C6-485E-AC35-66A374C73FAC"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:3.12:-:*:*:*:*:*:*", "matchCriteriaId": "5BAA3B29-CC59-41A5-AFBD-D7C24E65FC2F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*", "matchCriteriaId": "512EE3A8-A590-4501-9A94-5D4B268D6138"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/42fd831abfc15d0643c14688f0522556b347e7e6", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/4f0889f2df1ab99224a5e1ac4e20437eea5fe38e", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/663ce34786e759ebcbeb3060685c20bcc886d51a", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6b79abcb3c985e153fcf9d395e1d4336081aabc2", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/786e2c2a87d9c505f33321d1fd23a176aa8ddeb1", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/9d678eb0fe55c9195d9a253e8c5b82a87b930737", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, ... 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