Bug 2451190 (CVE-2026-23331)

Summary: CVE-2026-23331 kernel: udp: Unhash auto-bound connected sk from 4-tuple hash table when disconnected
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's handling of User Datagram Protocol (UDP) sockets. When an auto-bound UDP socket is connected and subsequently disconnected, it may not be properly unhashed from the 4-tuple hash table. This oversight can lead to the accumulation of stale entries, potentially causing resource exhaustion or performance degradation and resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-03-25 11:03:44 UTC 
In the Linux kernel, the following vulnerability has been resolved:

udp: Unhash auto-bound connected sk from 4-tuple hash table when disconnected.

Let's say we bind() an UDP socket to the wildcard address with a
non-zero port, connect() it to an address, and disconnect it from
the address.

bind() sets SOCK_BINDPORT_LOCK on sk->sk_userlocks (but not
SOCK_BINDADDR_LOCK), and connect() calls udp_lib_hash4() to put
the socket into the 4-tuple hash table.

Then, __udp_disconnect() calls sk->sk_prot->rehash(sk).

It computes a new hash based on the wildcard address and moves
the socket to a new slot in the 4-tuple hash table, leaving a
garbage in the chain that no packet hits.

Let's remove such a socket from 4-tuple hash table when disconnected.

Note that udp_sk(sk)->udp_portaddr_hash needs to be udpated after
udp_hash4_dec(hslot2) in udp_unhash4().
Comment 1 Alexander B 2026-03-25 17:12:59 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026032532-CVE-2026-23331-735b@gregkh/T