# CVE-2026-2858: wren-lang wren Source File wren_compiler.c peekChar out-of-bounds

> A local attacker can trigger an out-of-bounds read in the Wren compiler, potentially causing a denial of service.

- **Severity:** Medium 4.8 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P`)
- **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:** No
- **Published:** 20 Feb 2026
- **Updated:** 24 Feb 2026
- **Also known as:** GHSA-vm4c-6g35-79xf

## What is CVE-2026-2858?

CVE-2026-2858 is a medium-severity memory corruption vulnerability in wren-lang wren, published on 20 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability was identified in wren-lang wren up to 0.4.0. This affects the function peekChar of the file src/vm/wren_compiler.c of the component Source File Parser. Such manipulation leads to out-of-bounds read. The attack needs to be performed locally. The exploit is publicly available and might be used. The project was informed of the problem early through an issue report but has not responded yet.

Weakness: CWE-125 (Out-of-bounds Read), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2026-2858?

It affects 1 product.


Products: Wren Wren.

## How do I fix CVE-2026-2858?

No fix has been published for CVE-2026-2858 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-2858 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-2858 exists.

## Other vulnerabilities in wren-lang wren

- [CVE-2026-3385](https://insights.sbomify.com/CVE-2026-3385/): wren-lang wren wren_compiler.c resolveLocal recursion (medium 4.8)
- [CVE-2026-3386](https://insights.sbomify.com/CVE-2026-3386/): wren-lang wren wren_compiler.c emitOp out-of-bounds (medium 4.8)
- [CVE-2026-3387](https://insights.sbomify.com/CVE-2026-3387/): wren-lang wren wren_compiler.c getByteCountForArguments null pointer dereference (medium 4.8)
- [CVE-2026-2657](https://insights.sbomify.com/CVE-2026-2657/): wren-lang wren Error Message wren_compiler.c printError stack-based overflow (medium 4.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-2858 and fix it if it is affected.

What it is: CVE-2026-2858 is a medium-severity memory corruption vulnerability in wren-lang wren, published on 20 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-2858 exists.

Affected product: wren-lang wren. 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-2026-2858/ (Markdown: https://insights.sbomify.com/CVE-2026-2858/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-2858
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-2858
- OSV: https://osv.dev/vulnerability/CVE-2026-2858

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-2858/
Summaries are generated and may contain mistakes; the official description above is the record.