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PYSEC-2026-4161
restrictedpythonImpact
RestrictedPython could allow a sandbox escape when a policy exposes the standard library string module, or otherwise exposes string.Formatter, to restricted code.
string.Formatter field resolution methods such as get_field can perform attribute and item traversal internally and return live object references. This can bypass RestrictedPython's normal attribute guards and may allow access to sensitive objects such as function globals, builtins, file access, or code execution primitives.
Users are impacted if they run untrusted code with RestrictedPython and expose string.Formatter, directly or indirectly, for example through a custom import policy or globals.
Patches
The problem has been patched by blocking access to string.Formatter and unsafe string.Formatter traversal methods in safer_getattr.
Users should upgrade to the patched release once available. Affected and patched version numbers should be filled in when the release is published.
Workarounds
Do not expose the standard library string module or string.Formatter to restricted code.
If a custom import hook is used, deny imports of string or provide only a restricted wrapper that does not expose Formatter. If custom globals are supplied, ensure neither string.Formatter nor Formatter instances are available to restricted code.
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs high-level or administrative privileges. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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