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CVE-2026-76825: RestrictedPython: Sandbox escape via string.Formatter field resolution

• Severity: high (CVSS 8.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-16 · updated 2026-09-16
• Weakness: CWE-200

Description

RestrictedPython is a tool that helps define a subset of the Python language for accepting program input in a trusted environment. Prior to 8.4, RestrictedPython could allow a sandbox escape when a custom import policy or globals exposed the standard library string module, the string.Formatter class, a Formatter instance, or a Formatter subclass to restricted code. The string.Formatter methods format, get_field, get_value, and vformat performed attribute and item traversal internally without passing through RestrictedPython's safer_getattr protections. Restricted code could use those live object references to reach function globals, builtins, file access, or code execution primitives, affecting confidentiality, integrity, and availability in the host environment. This issue is fixed in version 8.4.

Affected products

• zopefoundation RestrictedPython: before 8.4

References

• https://github.com/zopefoundation/RestrictedPython/commit/3b47440070b91f8807c2b2998aca99e94783639a
• https://github.com/zopefoundation/RestrictedPython/releases/tag/8.4
• https://github.com/zopefoundation/RestrictedPython/security/advisories/GHSA-hp3v-5vw7-fx9w

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