CVE-2023-53585
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-10-04

Last updated on: 2026-03-23

Assigner: kernel.org

Description
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_FREE. 5. tcp_v4_rcv() skips sock_put(). Fix the problem by rejecting unhashed sockets in bpf_sk_assign(). This matches the behaviour of __inet_lookup_skb which is ultimately the goal of bpf_sk_assign().
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Meta Information
Published
2025-10-04
Last Modified
2026-03-23
Generated
2026-05-07
AI Q&A
2025-10-04
EPSS Evaluated
2026-05-05
NVD
CVE-2023-53585
EUVD
EUVD-2025-32324
Affected Vendors & Products
Showing 5 associated CPEs
Vendor Product Version / Range
linux linux_kernel From 6.5 (inc) to 6.5.3 (exc)
linux linux_kernel From 6.2 (inc) to 6.4.16 (exc)
linux linux_kernel From 5.16 (inc) to 6.1.53 (exc)
linux linux_kernel From 5.11 (inc) to 5.15.132 (exc)
linux linux_kernel From 5.7 (inc) to 5.10.195 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
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AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability involves the Linux kernel's bpf_sk_assign function, which improperly handles unhashed UDP sockets. The function assumes that the SOCK_RCU_FREE flag is never set between bpf_sk_assign and skb_steal_sock, but unhashed UDP sockets violate this assumption. This leads to a reference count leak because the socket's reference count is incremented but not properly decremented later, causing resource management issues. The fix was to reject unhashed sockets in bpf_sk_assign to prevent this leak.


How can this vulnerability impact me? :

The vulnerability can cause a reference count leak in the Linux kernel when handling certain UDP sockets, potentially leading to resource exhaustion or instability in the system. This could degrade system performance or cause unexpected behavior in network-related operations.


What immediate steps should I take to mitigate this vulnerability?

The vulnerability is fixed by rejecting unhashed sockets in the bpf_sk_assign helper function in the Linux kernel. To mitigate this vulnerability immediately, you should update your Linux kernel to a version that includes this fix. There are no specific configuration changes or commands provided to mitigate the issue other than applying the kernel patch or upgrade.


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