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

Vulnerability summary

CVE-2026-76825 is a high (CVSS 8.4) vulnerability in zopefoundation restrictedpython. EPSS estimates a 0.62% chance of exploitation in the next 30 days, higher than 49.9% of scored vulnerabilities.

Timeline

1. 16-09-2026
   PublishedVulnerability first disclosed.
2. 16-09-2026
   Last modifiedVulnerability information updated.

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.

• CWE-200Exposure of Sensitive Information to an Unauthorized ActorThe product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
• CWE-470Use of Externally-Controlled Input to Select Classes or CodeThe product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code.
• CWE-680Integer Overflow to Buffer OverflowThe product performs a calculation to determine how much memory to allocate, but an integer overflow can occur that causes less memory to be allocated than expected, leading to a buffer overflow.
• CWE-693Protection Mechanism FailureThe product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.