# CVE-2025-52566: llama.cpp tokenizer signed vs. unsigned heap overflow

> An attacker can trigger a heap overflow via manipulated text input in the llama.cpp tokenizer, potentially leading to code execution or denial of service.

- **Severity:** High 8.6 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 24 Jun 2025
- **Updated:** 24 Jun 2025
- **Also known as:** DEBIAN-CVE-2025-52566, GHSA-7rxv-5jhh-j6xx, OESA-2025-2371, OESA-2025-2372, OESA-2025-2373, UBUNTU-CVE-2025-52566

## What is CVE-2025-52566?

CVE-2025-52566 is a high-severity vulnerability in ggml-org llama.cpp, published on 24 Jun 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

llama.cpp is an inference of several LLM models in C/C++. Prior to version b5721, there is a signed vs. unsigned integer overflow in llama.cpp's tokenizer implementation (llama_vocab::tokenize) (src/llama-vocab.cpp:3036) resulting in unintended behavior in tokens copying size comparison. Allowing heap-overflowing llama.cpp inferencing engine with carefully manipulated text input during tokenization process. This issue has been patched in version b5721.

Weakness: CWE-195 (Signed to Unsigned Conversion Error), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2025-52566?

It affects 1 product.


Products: Ggml Llama.cpp.

## How do I fix CVE-2025-52566?

Upgrade to a fixed version.

## Is CVE-2025-52566 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-52566 exists.

## Other vulnerabilities in ggml-org llama.cpp

- [CVE-2024-42479](https://insights.sbomify.com/CVE-2024-42479/): llama.cpp allows write-what-where in rpc_server::set_tensor (critical 10.0)
- [CVE-2026-34159](https://insights.sbomify.com/CVE-2026-34159/): llama.cpp: Unauthenticated RCE via GRAPH_COMPUTE buffer=0 bypass in llama.cpp RPC backend (critical 9.8)
- [CVE-2026-43629](https://insights.sbomify.com/CVE-2026-43629/): llama.cpp b4882–b9058 Buffer Overflow in KV Cache State Restore (critical 9.2)
- [CVE-2026-43631](https://insights.sbomify.com/CVE-2026-43631/): llama.cpp b7492–b9060 Use-After-Free RCE via llama-server (critical 9.2)
- [CVE-2026-43632](https://insights.sbomify.com/CVE-2026-43632/): llama.cpp b7492–b9060 Use-After-Free in Tokenization Endpoints (critical 9.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-52566 and fix it if it is affected.

What it is: CVE-2025-52566 is a high-severity vulnerability in ggml-org llama.cpp, published on 24 Jun 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-52566 exists.

Affected product: ggml-org llama.cpp. 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-2025-52566/ (Markdown: https://insights.sbomify.com/CVE-2025-52566/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-52566
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-52566
- OSV: https://osv.dev/vulnerability/CVE-2025-52566

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From sbomify Insights: https://insights.sbomify.com/CVE-2025-52566/
Summaries are generated and may contain mistakes; the official description above is the record.