# CVE-2026-21869: llama.cpp has Out-of-bounds Write in llama-server

> Attackers can trigger out-of-bounds writes via negative parameters in llama.cpp server, potentially causing crashes or remote code execution.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 7 Jan 2026
- **Updated:** 8 Jan 2026
- **Also known as:** DEBIAN-CVE-2026-21869, GHSA-8947-pfff-2f3c, UBUNTU-CVE-2026-21869, openSUSE-SU-2026:10961-1

## What is CVE-2026-21869?

CVE-2026-21869 is a high-severity memory corruption vulnerability in ggml-org llama.cpp, published on 7 Jan 2026. An attacker can exploit it over the internet without logging in, 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++. In commits 55d4206c8 and prior, the n_discard parameter is parsed directly from JSON input in the llama.cpp server's completion endpoints without validation to ensure it's non-negative. When a negative value is supplied and the context fills up, llama_memory_seq_rm/add receives a reversed range and negative offset, causing out-of-bounds memory writes in the token evaluation loop. This deterministic memory corruption can crash the process or enable remote code execution (RCE). There is no fix at the time of publication.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-21869?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `llamacpp` | openSUSE:Tumbleweed | All versions | 9500-1.1 |

Products: Ggml Llama.cpp.

## How do I fix CVE-2026-21869?

No fix published yet.

## Is CVE-2026-21869 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21869 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-2026-21869 and fix it if it is affected.

What it is: CVE-2026-21869 is a high-severity memory corruption vulnerability in ggml-org llama.cpp, published on 7 Jan 2026. An attacker can exploit it over the internet without logging in, 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-2026-21869 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-2026-21869/ (Markdown: https://insights.sbomify.com/CVE-2026-21869/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21869
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21869
- OSV: https://osv.dev/vulnerability/CVE-2026-21869

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21869/
Summaries are generated and may contain mistakes; the official description above is the record.