# CVE-2023-53489: tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp.

> A memory leak in the Linux kernel network stack allows local attackers to exhaust system memory by closing sockets with specific timestamping and zerocopy options.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Oct 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-53489, DEBIAN-CVE-2023-53489, GHSA-5wf2-hxf9-8hxr, UBUNTU-CVE-2023-53489

## What is CVE-2023-53489?

CVE-2023-53489 is a medium-severity memory corruption vulnerability in Linux kernel, published on 1 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp.

syzkaller reported [0] memory leaks of an UDP socket and ZEROCOPY
skbs.  We can reproduce the problem with these sequences:

  sk = socket(AF_INET, SOCK_DGRAM, 0)
  sk.setsockopt(SOL_SOCKET, SO_TIMESTAMPING, SOF_TIMESTAMPING_TX_SOFTWARE)
  sk.setsockopt(SOL_SOCKET, SO_ZEROCOPY, 1)
  sk.sendto(b'', MSG_ZEROCOPY, ('127.0.0.1', 53))
  sk.close()

sendmsg() calls msg_zerocopy_alloc(), which allocates a skb, sets
skb->cb->ubuf.refcnt to 1, and calls sock_hold().  Here, struct
ubuf_info_msgzc indirectly holds a refcnt of the socket.  When the
skb is sent, __skb_tstamp_tx() clones it and puts the clone into
the socket's error queue with the TX timestamp.

When the original skb is received locally, skb_copy_ubufs() calls
skb_unclone(), and pskb_expand_head() increments skb->cb->ubuf.refcnt.
This additional count is decremented while freeing the skb, but struct
ubuf_info_msgzc still has a refcnt, so __msg_zerocopy_callback() is
not called.

The last refcnt is not released unless we retrieve the TX timestamped
skb by recvmsg().  Since we clear the error queue in inet_sock_destruct()
after the socket's refcnt reaches 0, there is a circular dependency.
If we close() the socket holding such skbs, we never call sock_put()
and leak the count, sk, and skb.

TCP has the same problem, and commit e0c8bccd40fc ("net: stream:
purge sk_error_queue in sk_stream_kill_queues()") tried to fix it
by calling skb_queue_purge() during close().  However, there is a
small chance that skb queued in a qdisc or device could be put
into the error queue after the skb_queue_purge() call.

In __skb_tstamp_tx(), the cloned skb should not have a reference
to the ubuf to remove the circular dependency, but skb_clone() does
not call skb_copy_ubufs() for zerocopy skb.  So, we need to call
skb_orphan_frags_rx() for the cloned skb to call skb_copy_ubufs().

[0]:
BUG: memory leak
unreferenced object 0xffff88800c6d2d00 (size 1152):
  comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 cd af e8 81 00 00 00 00  ................
    02 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00  ...@............
  backtrace:
    [<0000000055636812>] sk_prot_alloc+0x64/0x2a0 net/core/sock.c:2024
    [<0000000054d77b7a>] sk_alloc+0x3b/0x800 net/core/sock.c:2083
    [<0000000066f3c7e0>] inet_create net/ipv4/af_inet.c:319 [inline]
    [<0000000066f3c7e0>] inet_create+0x31e/0xe40 net/ipv4/af_inet.c:245
    [<000000009b83af97>] __sock_create+0x2ab/0x550 net/socket.c:1515
    [<00000000b9b11231>] sock_create net/socket.c:1566 [inline]
    [<00000000b9b11231>] __sys_socket_create net/socket.c:1603 [inline]
    [<00000000b9b11231>] __sys_socket_create net/socket.c:1588 [inline]
    [<00000000b9b11231>] __sys_socket+0x138/0x250 net/socket.c:1636
    [<000000004fb45142>] __do_sys_socket net/socket.c:1649 [inline]
    [<000000004fb45142>] __se_sys_socket net/socket.c:1647 [inline]
    [<000000004fb45142>] __x64_sys_socket+0x73/0xb0 net/socket.c:1647
    [<0000000066999e0e>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    [<0000000066999e0e>] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80
    [<0000000017f238c1>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

BUG: memory leak
unreferenced object 0xffff888017633a00 (size 240):
  comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 2d 6d 0c 80 88 ff ff  .........-m.....
  backtrace:
    [<000000002b1c4368>] __alloc_skb+0x229/0x320 net/core/skbuff.c:497
    [<00000000143579a6>] alloc_skb include/linux/skbuff.h:1265 [inline]
    [<00000000143579a6>] sock_omalloc+0xaa/0x190 net/core/sock.c:2596
    [<00000000be626478>] msg_zerocopy_alloc net/core/skbuff.c:1294 [inline]
    [<00000000be626478>]
---truncated---

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2023-53489?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-53489?

Apply the vendor's patch.

## Is CVE-2023-53489 being exploited?

There is no known exploitation of CVE-2023-53489 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-53489 and fix it if it is affected.

What it is: CVE-2023-53489 is a medium-severity memory corruption vulnerability in Linux kernel, published on 1 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-53489 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-53489/ (Markdown: https://insights.sbomify.com/CVE-2023-53489/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53489
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53489
- OSV: https://osv.dev/vulnerability/CVE-2023-53489

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53489/
Summaries are generated and may contain mistakes; the official description above is the record.