CVE-2023-41039

Sandbox escape via various forms of "format".

Workarounds

There are no workarounds to fix the issue without upgrading.

References

• https://docs.python.org/3/library/stdtypes.html#str.format_map
• http://lucumr.pocoo.org/2016/12/29/careful-with-str-format/
• https://www.exploit-db.com/exploits/51580

For more information

If you have any questions or comments about this advisory:

• Open an issue in the RestrictedPython issue tracker
• Email us at [email protected]

Credits

Thanks for analysing and reporting the go to:

• Abhishek Govindarasu
• Ankush Menat
• Ward Theunisse

Python's "format" functionality allows someone controlling the format string to "read" all objects accessible through recursive attribute lookup and subscription from objects he can access. This can lead to critical information disclosure.
With RestrictedPython, the format functionality is available via the format and format_map methods of str (and unicode) (accessed either via the class or its instances) and via string.Formatter.
All known versions of RestrictedPython are vulnerable.

CVE-2023-41039 has a CVSS score of 8.3 (High). The vector is network-reachable, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.4, 6.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

The issue will be fixed in 5.4 and 6.2.

1. What is CVE-2023-41039? CVE-2023-41039 is a high-severity security vulnerability in RestrictedPython (pip), affecting versions <= 5.3. It is fixed in 5.4, 6.2.
2. How severe is CVE-2023-41039? CVE-2023-41039 has a CVSS score of 8.3 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of RestrictedPython are affected by CVE-2023-41039? RestrictedPython (pip) versions <= 5.3 is affected.
4. Is there a fix for CVE-2023-41039? Yes. CVE-2023-41039 is fixed in 5.4, 6.2. Upgrade to this version or later.
5. Is CVE-2023-41039 exploitable, and should I be worried? Whether CVE-2023-41039 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-41039 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-41039?
   • Upgrade RestrictedPython to 5.4 or later
   • Upgrade RestrictedPython to 6.2 or later

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