Bug 2461753 (CVE-2026-31681)

Summary: CVE-2026-31681 kernel: netfilter: xt_multiport: validate range encoding in checkentry
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's netfilter xt_multiport module. This vulnerability arises from insufficient validation of range encoding within the `checkentry` function. A local attacker can exploit this by crafting malformed multiport rules, which causes the `ports_match_v1()` function to read beyond its intended memory boundary. This out-of-bounds read can lead to a denial of service (DoS) or potentially disclose sensitive information.
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Description OSIDB Bzimport 2026-04-25 09:01:18 UTC 
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.
Comment 1 Alexander B 2026-04-27 10:05:47 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042545-CVE-2026-31681-3c5b@gregkh/T