Vulnerability · Published Sep 14, 2026 · Assigned by GitHub_M
CVE-2026-55244ASTEVAL: Sandbox Escape via BaseException Subclasses
Medium 5.0
In plain English
A medium-severity security flaw in asteval from lmfit. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | python-asteval | no fix listed | DEBIAN-CVE-2026-55244 |
| Debian:13 | python-asteval | no fix listed | DEBIAN-CVE-2026-55244 |
| Debian:14 | python-asteval | no fix listed | DEBIAN-CVE-2026-55244 |
| PyPI | asteval | 1.0.9 | GHSA-89v8-rhwq-hf77 |
| PyPI | asteval | 1.0.9 | PYSEC-2026-3807 |
| Ubuntu:22.04:LTS | python-asteval | no fix listed | UBUNTU-CVE-2026-55244 |
| Ubuntu:24.04:LTS | python-asteval | no fix listed | UBUNTU-CVE-2026-55244 |
| Ubuntu:26.04:LTS | python-asteval | no fix listed | UBUNTU-CVE-2026-55244 |
| Ubuntu:26.10 | python-asteval | no fix listed | UBUNTU-CVE-2026-55244 |
Affected products (as reported)
Weakness: CWE-248 · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
References
- https://github.com/lmfit/asteval/security/advisories/GHSA-89v8-rhwq-hf77 x_refsource_CONFIRM
- https://github.com/lmfit/asteval/pull/153 x_refsource_MISC
- https://github.com/lmfit/asteval/commit/9c625b3674f8d05f206708bb85afca17a87694a4 x_refsource_MISC
- https://github.com/lmfit/asteval/commit/c49c99a67acb63eb7410231932250bd820380e45 x_refsource_MISC
- https://github.com/lmfit/asteval/releases/tag/1.0.9 x_refsource_MISC