Medium 5.5Published Apr 25, 2026

CVE-2026-31681netfilter: xt_multiport: validate range encoding in checkentry

Updated under an hour ago (Oct 28, 2026, 8:30 PM ET)

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Exploited in the last 30 days

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: 5.5 MEDIUM (v3.1, NVD)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): Not given
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Linux
NVD analysis: Modified
Record last updated: Oct 14, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Linux Linux linux:linux (from the name)	from a89ecb6a2ef732d04058d87801e2b6bd7e5c7089 before 8c5bf8f5b478f569191c4a7982de7cd5f5f73c1a; from a89ecb6a2ef732d04058d87801e2b6bd7e5c7089 before c9749f6232c845e31c21d4cc72200211df15d8a2; from a89ecb6a2ef732d04058d87801e2b6bd7e5c7089 before b67d638cbee9975c765feb45c126e96ed11ec802; from a89ecb6a2ef732d04058d87801e2b6bd7e5c7089 before 36bf0d98e180a7c384c8d8a59b0d2d4b80e5eb16; from a89ecb6a2ef732d04058d87801e2b6bd7e5c7089 before aec14808271f2bf2b656de6ff12dfe73c5fd3b67; from a89ecb6a2ef732d04058d87801e2b6bd7e5c7089 before 8368ce8eb01f0b91111d814703696e780d0ef12f; from a89ecb6a2ef732d04058d87801e2b6bd7e5c7089 before 1e4baa853f1cc4227e04f52d6860524707cfb294; from a89ecb6a2ef732d04058d87801e2b6bd7e5c7089 before ff64c5bfef12461df8450e0f50bb693b5269c720	CNA record
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518f_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem siemens:simatic_s7_1500_tm_mfp_gnu_linux_subsystem (from the name)	all versions	CISA ADP
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP siemens:siplus_s7_1500_cpu_1518_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
linux linux_kernel linux:linux_kernel	from 2.6.17 before 6.6.136; from 6.7 before 6.12.83; from 6.13 before 6.18.24; from 6.19 before 6.19.14; 7.0; 7.0; 7.0; 7.0; and 3 more ranges	NVD

References

References

https://git.kernel.org/stable/c/8c5bf8f5b478f569191c4a7982de7cd5f5f73c1a
https://git.kernel.org/stable/c/c9749f6232c845e31c21d4cc72200211df15d8a2
https://git.kernel.org/stable/c/b67d638cbee9975c765feb45c126e96ed11ec802
https://git.kernel.org/stable/c/36bf0d98e180a7c384c8d8a59b0d2d4b80e5eb16	patch
https://git.kernel.org/stable/c/aec14808271f2bf2b656de6ff12dfe73c5fd3b67	patch
https://git.kernel.org/stable/c/8368ce8eb01f0b91111d814703696e780d0ef12f	patch
https://git.kernel.org/stable/c/1e4baa853f1cc4227e04f52d6860524707cfb294	patch
https://git.kernel.org/stable/c/ff64c5bfef12461df8450e0f50bb693b5269c720	patch
https://cert-portal.siemens.com/productcert/html/ssa-019113.html
https://cert-portal.siemens.com/productcert/html/ssa-457936.html
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The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.