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CVE Record

CVE-2023-53585: bpf: reject unhashed sockets in bpf_sk_assign

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().

UnknownCVSS not scoredNot KEV-listedUpdated
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Security readout for executives and security teams

Plain-English summary

CVE-2023-53585 is a Linux kernel bug in BPF socket assignment handling. A specific UDP socket state can cause a socket reference count leak. The public record shows the kernel fix rejects unhashed sockets in this path. No active exploitation is indicated by KEV or the provided sources.

Executive priority

Treat as a planned kernel maintenance item unless your environment heavily uses BPF networking. There is no cited active exploitation or CVSS score, but kernel resource leaks can affect reliability. Patch through normal Linux update channels after vendor confirmation.

Technical view

The issue is in bpf_sk_assign(). It assumed SOCK_RCU_FREE would not change before skb_steal_sock. Unhashed UDP sockets can be added to sockmap, assigned, then bound or connected, changing SOCK_RCU_FREE and causing tcp_v4_rcv() to skip sock_put(), leaking a reference. Stable fixes reject unhashed sockets.

Likely exposure

Exposure is limited to Linux systems running affected kernel versions or downstream builds containing the vulnerable BPF behavior. The source lists Linux 5.7 through fixed stable releases, including 5.10.195, 5.15.132, 6.1.53, 6.4.16, 6.5.3, and 6.6 as affected markers.

Exploitation context

The provided sources describe a required sequence involving UDP sockets, sockmap, BPF socket lookup/assignment, and later bind or connect behavior. They do not state public exploitation, weaponized code, remote reachability, or required privileges. KEV status is false.

Researcher notes

The record identifies a refcount leak caused by changing SOCK_RCU_FREE state for unhashed UDP sockets after bpf_sk_assign. The fix aligns bpf_sk_assign behavior with __inet_lookup_skb by rejecting unhashed sockets. Public impact details beyond the leak are limited in the provided sources.

Mitigation direction

  • Update to a kernel build containing the referenced stable fixes.
  • Check your Linux distribution advisory for the corrected package version.
  • Prioritize systems that use BPF networking, sockmap, or custom traffic classification.
  • If patching is delayed, consult vendor guidance for supported risk-reduction options.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and container hosts.
  • Compare installed kernels with vendor advisories and the referenced stable commits.
  • Confirm the bpf_sk_assign fix is present in deployed kernel source or changelog.
  • Review environments for BPF sockmap or traffic-control BPF usage.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2023-53585 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
7Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxcf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449, cf7fbe660f2dbd738ab58aea8e9b0ca6ad232449unaffected
LinuxLinux5.7, 0, 5.10.195, 5.15.132, 6.1.53, 6.4.16, 6.5.3, 6.6affected
Weakness

CWE details

No CWE listed

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