RestrictedPython guard hooks can be shadowed via positional-only arguments

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.3 · CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:L

EPSS

• CVE-2026-55830: 0.29% estimated exploitation activity in the next 30 days; percentile 21.25 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact RestrictedPython rewrites sensitive operations to go through guard hooks. Attribute access becomes getattr(obj, name), item access becomes getitem(obj, key), writes go through write, and print goes through print. The embedding application supplies these hooks to enforce its policy. Argument-name validation rejects these protected names for regular arguments, args, kwargs, and keyword-only arguments, but it misses positional-only arguments (the ones before /). So a function like: makes getattr a local that shadows the policy hook, and the rewritten access calls evil instead. The same works for getitem, write, and print. Shadowing print can also be used to capture the internal getattr hook that RestrictedPython passes in. The result is that sandboxed code can bypass the access policy the embedding application relies on. In applications that also handle sandbox-controlled objects unsafely (for example serializing them with pickle), this primitive can be chained further, up to…

Published by the source

28 Aug 2026, 22:51 UTC

Last modified by the source

28 Aug 2026, 22:51 UTC

Source last checked

26 Oct 2026, 13:50 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-ffg3-p8fm-mjx2

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# Patch Next advisory brief: CVE-2026-55830

Advisory: RestrictedPython guard hooks can be shadowed via positional-only arguments
IDs: CVE-2026-55830, GHSA-ffg3-p8fm-mjx2
Record: https://patchnext.com/advisories/cve-2026-55830 (revision 1, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: restrictedpython 8.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI restrictedpython: affected <= 8.2; fixed in 8.3

## Suggested inspection (read-only)
- `python -m pip show restrictedpython`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on restrictedpython.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-ffg3-p8fm-mjx2 (GitHub-reviewed advisory GHSA-ffg3-p8fm-mjx2 lists affected ranges: PyPI restrictedpython >=0 <=8.2)

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