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.
- 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
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
Which versions are affected by CVE-2026-55244?
3 open source packages ship an affected version, including asteval.
| Package | Affected | Fixed in |
|---|---|---|
asteval PyPI | All versions | 1.0.9 |
asteval PyPI | All versions | 1.0.9 |
asteval PyPI | All versions | 1.0.9 |
Linux distribution packages (1)
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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-55244 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55244 exists.
Sources
Also known as DEBIAN-CVE-2026-55244, GHSA-89v8-rhwq-hf77, PYSEC-2026-3807, UBUNTU-CVE-2026-55244, openSUSE-SU-2026:11420-1.