# CVE-2026-55244: ASTEVAL: Sandbox Escape via BaseException Subclasses

> Attackers can cause denial of service in applications using ASTEVAL by raising specific BaseException subclasses that bypass safety handlers.

- **Severity:** Medium 5.0 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 14 Sep 2026
- **Updated:** 16 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-55244, GHSA-89v8-rhwq-hf77, PYSEC-2026-3807, UBUNTU-CVE-2026-55244, openSUSE-SU-2026:11420-1

## What is CVE-2026-55244?

CVE-2026-55244 is a medium-severity denial of service vulnerability in lmfit asteval, published on 14 Sep 2026. 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

ASTEVAL is an evaluator of Python expressions and statements. Prior to 1.0.9, FROM_PY in asteval/astutils.py exposes BaseException, SystemExit, KeyboardInterrupt, and GeneratorExit to expressions evaluated by asteval.Interpreter.eval(), while run() and eval() in asteval/asteval.py catch Exception rather than these non-Exception BaseException subclasses. When an attacker-controlled expression raises one of these classes, on_raise() passes the class to raise_exception(), and the resulting exception bypasses the interpreter's safety handlers and propagates into the calling application. A consuming service that evaluates untrusted expressions can therefore be terminated or have signal and cleanup handling disrupted, causing denial of service. The separately documented read-only open() capability is not part of this vulnerability. This issue is fixed in version 1.0.9.

Weakness: CWE-248 (Uncaught Exception)

## Which versions are affected by CVE-2026-55244?

3 open source packages ship an affected version, including asteval.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `asteval` | PyPI | All versions | 1.0.9 |
| `asteval` | PyPI | All versions | 1.0.9 |
| `asteval` | PyPI | All versions | 1.0.9 |
| `python-asteval` | openSUSE:Tumbleweed | All versions | 1.0.9-1.1 |

## How do I fix CVE-2026-55244?

Upgrade asteval to 1.0.9 or later.

## Is CVE-2026-55244 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55244 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55244 and fix it if it is affected.

What it is: CVE-2026-55244 is a medium-severity denial of service vulnerability in lmfit asteval, published on 14 Sep 2026. 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-2026-55244 exists.

Affected packages and fixed versions:
- asteval (PyPI): affected all versions; fixed in 1.0.9
- asteval (PyPI): affected all versions; fixed in 1.0.9
- asteval (PyPI): affected all versions; fixed in 1.0.9

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-2026-55244/ (Markdown: https://insights.sbomify.com/CVE-2026-55244/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55244
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55244
- OSV: https://osv.dev/vulnerability/CVE-2026-55244

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-55244/
Summaries are generated and may contain mistakes; the official description above is the record.