CVE-2026-6386

Description

In order to apply a particular protection key to an address range, the kernel must update the corresponding page table entries. The subroutine which handled this failed to take into account the presence of 1GB largepage mappings created using the shm_create_largepage(3) interface. In particular, it would always treat a page directory page entry as pointing to another page table page. The bug can be abused by an unprivileged user to cause pmap_pkru_update_range() to treat userspace memory as a page table page, and thus overwrite memory to which the application would otherwise not have access.

CVSS Details

CVSS Score

6.2

Severity

MEDIUM

CVSS Vector

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

Configurations (Affected Products)

cpe:2.3:o:freebsd:freebsd:13.5:-:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:freebsd:freebsd:13.5:beta3:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:freebsd:freebsd:13.5:p1:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:freebsd:freebsd:13.5:p10:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:freebsd:freebsd:13.5:p11:*:*:*:*:*:* - VULNERABLE

FreeBSD (具体受影响版本请参考官方安全公告 FreeBSD-SA-26:11)

PoC / Exploit Code

⚠ For Security Research Only

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

python

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/shm.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

// Conceptual Proof of Concept for CVE-2026-6386
// Demonstrates triggering the largepage pmap bug

int main() {
    int shmid;
    void *addr;
    size_t size = 1UL << 30; // 1GB

    // Create a shared memory segment
    // In a real exploit, this would leverage shm_create_largepage(3) or specific flags
    shmid = shmget(IPC_PRIVATE, size, IPC_CREAT | IPC_EXCL | 0600);
    if (shmid < 0) {
        perror("shmget failed");
        return 1;
    }

    // Attach the shared memory to the address space
    addr = shmat(shmid, NULL, 0);
    if (addr == (void *)-1) {
        perror("shmat failed");
        return 1;
    }

    printf("Memory mapped at %p\n", addr);

    // Trigger the vulnerable path: pmap_pkru_update_range
    // This involves manipulating memory protection keys (pkeys) on the mapped region.
    // The kernel will treat the largepage directory entry as a page table entry,
    // leading to the corruption.
    
    // Note: Actual exploitation requires precise memory layout and pkey usage.
    #ifdef __FreeBSD__
    // Hypothetical trigger logic
    // pkey_mprotect(addr, size, PROT_READ, pkey);
    #endif

    printf("Vulnerability triggered. Check kernel logs for crash or corruption.\n");
    
    // Cleanup
    shmdt(addr);
    shmctl(shmid, IPC_RMID, NULL);
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-6386
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-6386
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-6386/
[4] VulDB https://vuldb.com/cve/CVE-2026-6386
[5] https://security.freebsd.org/advisories/FreeBSD-SA-26:11.amd64.asc

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-6386", "sourceIdentifier": "[email protected]", "published": "2026-04-22T03:16:01.313", "lastModified": "2026-05-01T12:49:08.827", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In order to apply a particular protection key to an address range, the kernel must update the corresponding page table entries. The subroutine which handled this failed to take into account the presence of 1GB largepage mappings created using the shm_create_largepage(3) interface. In particular, it would always treat a page directory page entry as pointing to another page table page.\n\nThe bug can be abused by an unprivileged user to cause pmap_pkru_update_range() to treat userspace memory as a page table page, and thus overwrite memory to which the application would otherwise not have access."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N", "baseScore": 6.2, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.5, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-269"}, {"lang": "en", "value": "CWE-732"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:-:*:*:*:*:*:*", "matchCriteriaId": "947F561E-AD65-43B9-94C1-3109A3D35248"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:beta3:*:*:*:*:*:*", "matchCriteriaId": "4216D505-95A5-4FCC-8B9A-26FCD32B0445"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p1:*:*:*:*:*:*", "matchCriteriaId": "3D1987F1-1E08-4B28-8D16-D25A091D99ED"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p10:*:*:*:*:*:*", "matchCriteriaId": "4C859EE2-59C0-4234-BFF0-7794AC4956DD"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p11:*:*:*:*:*:*", "matchCriteriaId": "D1CEB391-5FA3-4FFD-9279-113093DD500D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p2:*:*:*:*:*:*", "matchCriteriaId": "BEC1E8A0-0402-45F1-938D-FEFDCFC3E747"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p3:*:*:*:*:*:*", "matchCriteriaId": "D94457D6-738F-4ABB-BD46-F2B621531FE2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p4:*:*:*:*:*:*", "matchCriteriaId": "8C38CB56-B80C-4D1B-9267-16E8F985B170"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p5:*:*:*:*:*:*", "matchCriteriaId": "13DF1E38-5E8D-42FF-A4C5-092300864F3E"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p6:*:*:*:*:*:*", "matchCriteriaId": "83A86F81-0965-4600-835A-496756137998"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p7:*:*:*:*:*:*", "matchCriteriaId": "987E31A4-7E21-471E-A3EA-4E53FFDB3DFB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p8:*:*:*:*:*:*", "matchCriteriaId": "9FBFE8B3-DC7C-4394-B062-C40E201EC059"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:13.5:p9:*:*:*:*:*:*", "matchCriteriaId": "563C1D65-625D-43FC-A7A0-75B1E2163C40"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:-:*:*:*:*:*:*", "matchCriteriaId": "9DC7C54E-58AF-4ADE-84AF-0EF0F325E20E"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p1:*:*:*:*:*:*", "matchCriteriaId": "D3D22B8C-36CF-4800-9673-0B0240558BDD"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p10:*:*:*:*:*:*", "matchCriteriaId": "7296F5AA-F8C1-4277-A4EE-C2B24073A320"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p2:*:*:*:*:*:*", "matchCriteriaId": "242FA2A8-5D7D-4617-A411-2651FF3A3E4C"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p3:*:*:*:*:*:*", "matchCriteriaId": "40573F60-F3B7-4AEC-846A-B08E5B7D9D00"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p4:*:*:*:*:*:*", "matchCriteriaId": "1FB832CE-0A98-44A2-8BAC-CD38A64279B6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p5:*:*:*:*:*:*", "matchCriteriaId": "9A785F8E-C218-41AE-8D57-BF06DDAEF7CB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p6:*:*:*:*:*:*", "matchCriteriaId": "C3909FDD-B2A2-45B6-A40B-1D303A717F15"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p7:*:*:*:*:*:*", "matchCriteriaId": "720597A2-F181-46E1-8A0D-097E17ADC4FB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p8:*:*:*:*:*:*", "matchCriteriaId": "DC8A75D0-148A-427A-9783-45477EABED21"}, {"vulnerable": true, "criteria": "cpe:2.3:o:freebsd:freebsd:14.3:p9:*:*:*:*:*:*", "matchCriteriaId": "F5D39FC9-6DBA-46C8-BB80-A ... 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