# CVE-2026-100864: heym before 0.0.91 Remote Code Execution via Expression Engine

> Authenticated attackers can execute arbitrary Python code via sandbox escape in the expression engine of the heym library.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 Sep 2026
- **Updated:** 28 Sep 2026
- **Also known as:** GHSA-87x2-9jwx-7gh4, GHSA-gxgj-2794-2q5v

## What is CVE-2026-100864?

CVE-2026-100864 is a high-severity code injection vulnerability in heymrun heym, published on 27 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

heym before 0.0.91 contains a sandbox escape vulnerability in the expression engine's DotList map/filter and fallback resolver that allows authenticated users to execute arbitrary Python code. Attackers can craft workflow expressions using dunder attribute access through item expressions or the fallback resolver to access os.system and execute commands as the backend process.

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-100864?


## How do I fix CVE-2026-100864?

No fix has been published for CVE-2026-100864 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100864 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100864 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100864 and fix it if it is affected.

What it is: CVE-2026-100864 is a high-severity code injection vulnerability in heymrun heym, published on 27 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100864 exists.

Affected product: heymrun heym. 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-2026-100864/ (Markdown: https://insights.sbomify.com/CVE-2026-100864/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100864
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100864
- OSV: https://osv.dev/vulnerability/CVE-2026-100864

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-100864/
Summaries are generated and may contain mistakes; the official description above is the record.