CVE-2026-31681

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: xt_multiport: validate range encoding in checkentry ports_match_v1() treats any non-zero pflags entry as the start of a port range and unconditionally consumes the next ports[] element as the range end. The checkentry path currently validates protocol, flags and count, but it does not validate the range encoding itself. As a result, malformed rules can mark the last slot as a range start or place two range starts back to back, leaving ports_match_v1() to step past the last valid ports[] element while interpreting the rule. Reject malformed multiport v1 rules in checkentry by validating that each range start has a following element and that the following element is not itself marked as another range start.

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

cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:* - VULNERABLE

Linux Kernel (多个稳定版本，具体受影响版本请参考Git提交记录)

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * PoC Concept for CVE-2026-31681
 * Trigger: Kernel panic via malformed iptables multiport rule
 */
#include <stdio.h>
#include <string.h>

// Conceptual structure of the vulnerable rule data
struct xt_multiport_v1 {
    __u8 flags;          // Flags indicating range start
    __u8 count;          // Number of ports
    __u16 ports[];       // Port array
};

int main() {
    printf("[*] CVE-2026-31681 PoC Concept\n");
    printf("[*] Vulnerability: xt_multiport lacks range validation in checkentry\n");
    printf("[*] Impact: Out-of-bounds read in ports_match_v1 leading to DoS\n\n");

    // To trigger this, one would typically use netlink to add a rule
    // where the last port has a range flag set (IP6T_MULTIPORT_RANGE),
    // forcing the kernel to read past the allocated ports array.

    printf("[!] Exploitation requires sending a malformed netlink message\n");
    printf("[!] or modifying iptables tool to bypass user-space checks.\n");
    printf("[!] Example payload logic: Set range flag on last port index.\n");

    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31681
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31681
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31681/
[4] VulDB https://vuldb.com/cve/CVE-2026-31681
[5] https://git.kernel.org/stable/c/1e4baa853f1cc4227e04f52d6860524707cfb294
[6] https://git.kernel.org/stable/c/36bf0d98e180a7c384c8d8a59b0d2d4b80e5eb16
[7] https://git.kernel.org/stable/c/8368ce8eb01f0b91111d814703696e780d0ef12f
[8] https://git.kernel.org/stable/c/aec14808271f2bf2b656de6ff12dfe73c5fd3b67
[9] https://git.kernel.org/stable/c/ff64c5bfef12461df8450e0f50bb693b5269c720

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31681", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-25T09:16:01.800", "lastModified": "2026-05-06T21:21:50.587", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: xt_multiport: validate range encoding in checkentry\n\nports_match_v1() treats any non-zero pflags entry as the start of a\nport range and unconditionally consumes the next ports[] element as\nthe range end.\n\nThe checkentry path currently validates protocol, flags and count, but\nit does not validate the range encoding itself. As a result, malformed\nrules can mark the last slot as a range start or place two range starts\nback to back, leaving ports_match_v1() to step past the last valid\nports[] element while interpreting the rule.\n\nReject malformed multiport v1 rules in checkentry by validating that\neach range start has a following element and that the following element\nis not itself marked as another range start."}], "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": "2.6.17", "versionEndExcluding": "6.6.136", "matchCriteriaId": "A7B9FFD8-E991-452F-9730-FADDA1A54E82"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.83", "matchCriteriaId": "7F0AE5B5-23AC-4DCC-B37A-51CA1DAE7BA8"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.24", "matchCriteriaId": "8126B8B8-6D0B-4443-86C1-672AEE893555"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.14", "matchCriteriaId": "D6A8A074-BBF4-4803-ABED-519A839435BB"}, {"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/1e4baa853f1cc4227e04f52d6860524707cfb294", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/36bf0d98e180a7c384c8d8a59b0d2d4b80e5eb16", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/8368ce8eb01f0b91111d814703696e780d0ef12f", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/aec14808271f2bf2b656de6ff12dfe73c5fd3b67", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/ff64c5bfef12461df8450e0f50bb693b5269c720", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}