Skip to content
Fencer Vulns
medium 5.5

CVE-2023-53585 json

bpf: reject unhashed sockets in bpf_sk_assign

published 2025-10-04 13 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-32324

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 5%
public exploits
0
none known

Summary

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().

Patch / fix

  • Linux Linux 5.10.195, 5.15.132, 6.1.53, 6.4.16, 6.5.3, 6.6
  • linux Debian 12 6.1.55-1
  • linux Debian 14, Debian 13 6.5.3-1

debian advisories DEBIAN-CVE-2023-53585

  • linux Ubuntu 22.04 LTS 5.15.0-94.104
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1053.58
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1051.59
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1050.55
  • linux-ibm Ubuntu 22.04 LTS 5.15.0-1046.49
  • linux-kvm Ubuntu 22.04 LTS 5.15.0-1050.55
  • linux-azure Ubuntu 22.04 LTS 5.15.0-1056.64
  • linux-gkeop Ubuntu 22.04 LTS 5.15.0-1036.42

ubuntu advisories UBUNTU-CVE-2023-53585

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 9 5.14.0-427.13.1.el9_4
  • rv RHEL 9 5.14.0-427.13.1.el9_4
  • perf RHEL 9 5.14.0-427.13.1.el9_4
  • rtla RHEL 9 5.14.0-427.13.1.el9_4
  • bpftool RHEL 9 7.3.0-427.13.1.el9_4
  • libperf RHEL 9 5.14.0-427.13.1.el9_4
  • kernel-rt RHEL 9 5.14.0-427.13.1.el9_4
  • kernel-64k RHEL 9 5.14.0-427.13.1.el9_4

red hat advisories RHSA-2024:2394RHSA-2020:4431

  • kernel-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.58.1
  • kernel-syms-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.58.1
  • kernel-rt_debug Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.58.1
  • kernel-source-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.58.1
  • kernel-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-38.1
  • kernel-source-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-38.1
  • kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.22.1
  • kernel-syms-rt Real Time Module 15 SP7 6.4.0-150700.7.22.1

suse advisories SUSE-SU-2025:4301-1SUSE-SU-2025:21052-1SUSE-SU-2025:21064-1SUSE-SU-2025:4141-1SUSE-SU-2025:4140-1SUSE-SU-2025:4132-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-53585 updated cvss 5.5

kernel: bpf: reject unhashed sockets in bpf_sk_assign

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +6 more Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    affected: no fix available “Fix deferred”
  • Red Hat CodeReady Linux Builder (v. 8) kernel-debuginfo-common-x86_64 4.18.0-240.el8, kernel-debuginfo-common-aarch64 4.18.0-240.el8, kernel-debuginfo-common-ppc64le 4.18.0-240.el8
    fixed: vendor fix RHSA-2020:4431
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-427.13.1.el9_4, perf 5.14.0-427.13.1.el9_4, rtla 5.14.0-427.13.1.el9_4, kernel-devel-matched 5.14.0-427.13.1.el9_4, kernel-64k-devel-matched 5.14.0-427.13.1.el9_4, kernel-debug-devel-matched 5.14.0-427.13.1.el9_4, +6 more
    fixed: vendor fix RHSA-2024:2394
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-240.el8, kernel 4.18.0-240.el8, bpftool 4.18.0-240.el8, kernel-core 4.18.0-240.el8, kernel-tools 4.18.0-240.el8, python3-perf 4.18.0-240.el8, +15 more
    fixed: vendor fix RHSA-2020:4431
  • Red Hat Enterprise Linux BaseOS (v. 9) bpftool 7.3.0-427.13.1.el9_4, kernel 5.14.0-427.13.1.el9_4, kernel-64k 5.14.0-427.13.1.el9_4, kernel-core 5.14.0-427.13.1.el9_4, kernel-tools 5.14.0-427.13.1.el9_4, python3-perf 5.14.0-427.13.1.el9_4, +28 more Red Hat Enterprise Linux CRB (v. 9) libperf 5.14.0-427.13.1.el9_4, kernel-debuginfo-common-s390x 5.14.0-427.13.1.el9_4, kernel-debuginfo-common-x86_64 5.14.0-427.13.1.el9_4, kernel-debuginfo-common-aarch64 5.14.0-427.13.1.el9_4, kernel-debuginfo-common-ppc64le 5.14.0-427.13.1.el9_4 Red Hat Enterprise Linux NFV (v. 9) kernel-rt 5.14.0-427.13.1.el9_4, kernel-rt-kvm 5.14.0-427.13.1.el9_4, kernel-rt-core 5.14.0-427.13.1.el9_4, kernel-rt-modules 5.14.0-427.13.1.el9_4, kernel-rt-debug-kvm 5.14.0-427.13.1.el9_4, kernel-rt-debug-core 5.14.0-427.13.1.el9_4, +6 more Red Hat Enterprise Linux RT (v. 9) kernel-rt 5.14.0-427.13.1.el9_4, kernel-rt-core 5.14.0-427.13.1.el9_4, kernel-rt-modules 5.14.0-427.13.1.el9_4, kernel-rt-debug-core 5.14.0-427.13.1.el9_4, kernel-rt-modules-core 5.14.0-427.13.1.el9_4, kernel-rt-debug-modules 5.14.0-427.13.1.el9_4, +4 more
    fixed: vendor fix RHSA-2024:2394
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 10 kernel
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.16% chance of exploitation in the next 30 days, higher than 5% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.