CVE-2023-53585

published 2025-10-04

CVE-2023-53585: In the Linux kernel, the following vulnerability has been resolved: bpf: reject unhashed sockets in bpf_sk_assign The semantics for bpf_sk_assign are as…

Priority P4 21 medium 5.5 CVSS 3.1

AV L AC L PR L UI N S U C N I N A H

In the Linux kernel, the following vulnerability has been resolved:

bpf: reject unhashed sockets in bpf_sk_assign

The semantics for bpf_sk_assign are as follows:

sk = some_lookup_func()
bpf_sk_assign(skb, sk)
bpf_sk_release(sk)

That is, the sk is not consumed by bpf_sk_assign. The function
therefore needs to make sure that sk lives long enough to be
consumed from __inet_lookup_skb. The path through the stack for a
TCPv4 packet is roughly:

netif_receive_skb_core: takes RCU read lock
__netif_receive_skb_core:
sch_handle_ingress:
tcf_classify:
bpf_sk_assign()
deliver_ptype_list_skb:
deliver_skb:
ip_packet_type->func == ip_rcv:
ip_rcv_core:
ip_rcv_finish_core:
dst_input:
ip_local_deliver:
ip_local_deliver_finish:
ip_protocol_deliver_rcu:
tcp_v4_rcv:
__inet_lookup_skb:
skb_steal_sock

The existing helper takes advantage of the fact that everything
happens in the same RCU critical section: for sockets with
SOCK_RCU_FREE set bpf_sk_assign never takes a reference.
skb_steal_sock then checks SOCK_RCU_FREE again and does sock_put
if necessary.

This approach assumes that SOCK_RCU_FREE is never set on a sk
between bpf_sk_assign and skb_steal_sock, but this invariant is
violated by unhashed UDP sockets. A new UDP socket is created
in TCP_CLOSE state but without SOCK_RCU_FREE set. That flag is only
added in udp_lib_get_port() which happens when a socket is bound.

When bpf_sk_assign was added it wasn't possible to access unhashed
UDP sockets from BPF, so this wasn't a problem. This changed
in commit 0c48eefae712 ("sock_map: Lift socket state restriction
for datagram sockets"), but the helper wasn't adjusted accordingly.
The following sequence of events will therefore lead to a refcount
leak:

1. Add socket(AF_INET, SOCK_DGRAM) to a sockmap.
2. Pull socket out of sockmap and bpf_sk_assign it. Since
SOCK_RCU_FREE is not set we increment the refcount.
3. bind() or connect() the socket, setting SOCK_RCU_FREE.
4. skb_steal_sock will now set refcounted = false due to
SOCK_RCU_FRE

Affected

17 ranges

Vendor	Product	Version range	Fixed in
debian	linux	< linux 6.1.55-1 (bookworm)	linux 6.1.55-1 (bookworm)
linux	linux	—	—
linux	linux	>= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 < 791a12102e5191dcb6ce0b3a99d71b5a2802d12a	791a12102e5191dcb6ce0b3a99d71b5a2802d12a
linux	linux	>= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 < 7dcbc0bb0e5cc1823923744befce59ac353135e6	7dcbc0bb0e5cc1823923744befce59ac353135e6
linux	linux	>= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 < c0ce0fb76610d5fad31f56f2ca8241a2a6717a1b	c0ce0fb76610d5fad31f56f2ca8241a2a6717a1b
linux	linux	>= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 < 8aa43cfbb68b25119d2ced14ec717173e2901fa2	8aa43cfbb68b25119d2ced14ec717173e2901fa2
linux	linux	>= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 < 3d4522f59fb748a54446846522941a4f09da63e9	3d4522f59fb748a54446846522941a4f09da63e9
linux	linux	>= cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449 < 67312adc96b5a585970d03b62412847afe2c6b01	67312adc96b5a585970d03b62412847afe2c6b01
linux	linux_kernel	>= 0 < 5.10.197-1	5.10.197-1
linux	linux_kernel	>= 0 < 6.1.55-1	6.1.55-1
linux	linux_kernel	>= 0 < 6.5.3-1	6.5.3-1
linux	linux_kernel	>= 0 < 6.5.3-1	6.5.3-1
linux	linux_kernel	>= 5.11 < 5.15.132	5.15.132
linux	linux_kernel	>= 5.16 < 6.1.53	6.1.53
linux	linux_kernel	>= 5.7 < 5.10.195	5.10.195
linux	linux_kernel	>= 6.2 < 6.4.16	6.4.16
linux	linux_kernel	>= 6.5 < 6.5.3	6.5.3

CVSS provenance

nvd v3.1 5.5 MEDIUM CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

osv 5.5 MEDIUM

vendor_debian 5.5 MEDIUM

vendor_redhat 5.5 MEDIUM

Stop checking back — get the weekly exploitation signal.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.

CWE-911