# CVE-2026-31681

> Vulnerability · severity: **MEDIUM** (CVSS 5.5).

## 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.

## Key facts

- **CVE ID:** CVE-2026-31681
- **Published:** 2026-04-25
- **CVSS severity:** MEDIUM
- **CVSS base score:** 5.5
- **CWE codes:** NVD-CWE-noinfo

## Affected products

- `linux:linux_kernel`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31681

## Citation

> AI Analytics. CVE-2026-31681. Retrieved 2026-08-17 from https://api.ai-analytics.org/cve/CVE-2026-31681. Derived from NIST NVD. Licensed CC0.

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