# CVE-2023-53024: bpf: Fix pointer-leak due to insufficient speculative store bypass mitigation

> An attacker can leak kernel pointer values via speculative execution side channels in the Linux kernel BPF subsystem.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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:** 27 Mar 2025
- **Updated:** 23 May 2026
- **Also known as:** BELL-CVE-2023-53024, DEBIAN-CVE-2023-53024, GHSA-mqh3-5x68-9v64, UBUNTU-CVE-2023-53024

## What is CVE-2023-53024?

CVE-2023-53024 is a high-severity vulnerability in Linux kernel, published on 27 Mar 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:

bpf: Fix pointer-leak due to insufficient speculative store bypass mitigation

To mitigate Spectre v4, 2039f26f3aca ("bpf: Fix leakage due to
insufficient speculative store bypass mitigation") inserts lfence
instructions after 1) initializing a stack slot and 2) spilling a
pointer to the stack.

However, this does not cover cases where a stack slot is first
initialized with a pointer (subject to sanitization) but then
overwritten with a scalar (not subject to sanitization because
the slot was already initialized). In this case, the second write
may be subject to speculative store bypass (SSB) creating a
speculative pointer-as-scalar type confusion. This allows the
program to subsequently leak the numerical pointer value using,
for example, a branch-based cache side channel.

To fix this, also sanitize scalars if they write a stack slot
that previously contained a pointer. Assuming that pointer-spills
are only generated by LLVM on register-pressure, the performance
impact on most real-world BPF programs should be small.

The following unprivileged BPF bytecode drafts a minimal exploit
and the mitigation:

  [...]
  // r6 = 0 or 1 (skalar, unknown user input)
  // r7 = accessible ptr for side channel
  // r10 = frame pointer (fp), to be leaked
  //
  r9 = r10 # fp alias to encourage ssb
  *(u64 *)(r9 - 8) = r10 // fp[-8] = ptr, to be leaked
  // lfence added here because of pointer spill to stack.
  //
  // Ommitted: Dummy bpf_ringbuf_output() here to train alias predictor
  // for no r9-r10 dependency.
  //
  *(u64 *)(r10 - 8) = r6 // fp[-8] = scalar, overwrites ptr
  // 2039f26f3aca: no lfence added because stack slot was not STACK_INVALID,
  // store may be subject to SSB
  //
  // fix: also add an lfence when the slot contained a ptr
  //
  r8 = *(u64 *)(r9 - 8)
  // r8 = architecturally a scalar, speculatively a ptr
  //
  // leak ptr using branch-based cache side channel:
  r8 &= 1 // choose bit to leak
  if r8 == 0 goto SLOW // no mispredict
  // architecturally dead code if input r6 is 0,
  // only executes speculatively iff ptr bit is 1
  r8 = *(u64 *)(r7 + 0) # encode bit in cache (0: slow, 1: fast)
SLOW:
  [...]

After running this, the program can time the access to *(r7 + 0) to
determine whether the chosen pointer bit was 0 or 1. Repeat this 64
times to recover the whole address on amd64.

In summary, sanitization can only be skipped if one scalar is
overwritten with another scalar. Scalar-confusion due to speculative
store bypass can not lead to invalid accesses because the pointer
bounds deducted during verification are enforced using branchless
logic. See 979d63d50c0c ("bpf: prevent out of bounds speculation on
pointer arithmetic") for details.

Do not make the mitigation depend on !env->allow_{uninit_stack,ptr_leaks}
because speculative leaks are likely unexpected if these were enabled.
For example, leaking the address to a protected log file may be acceptable
while disabling the mitigation might unintentionally leak the address
into the cached-state of a map that is accessible to unprivileged
processes.

## Which versions are affected by CVE-2023-53024?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-53024?

Apply the vendor's patch.

## Is CVE-2023-53024 being exploited?

There is no known exploitation of CVE-2023-53024 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-2023-53024 and fix it if it is affected.

What it is: CVE-2023-53024 is a high-severity vulnerability in Linux kernel, published on 27 Mar 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-2023-53024 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-2023-53024/ (Markdown: https://insights.sbomify.com/CVE-2023-53024/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53024
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53024
- OSV: https://osv.dev/vulnerability/CVE-2023-53024

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53024/
Summaries are generated and may contain mistakes; the official description above is the record.