A flaw in Node.js Permission Model filesystem enforcement leaves fs.realpathSync() without the required read permission checks. This is an incomplete fix of CVE-2026-21715, which only covered fs.realpathSync.native().
As a result, code running under --permission with restricted --allow-fs-read can still use fs.realpathSync() to check file existence, resolve symlink targets, and enumerate filesystem paths outside of permitted directories.
This vulnerability affects Node.js 26.x, 24.x, and 22.x.
Weakness
The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
Extended Description
Access control involves the use of several protection mechanisms such as:
When any mechanism is not applied or otherwise fails, attackers can compromise the security of the product by gaining privileges, reading sensitive information, executing commands, evading detection, etc. There are two distinct behaviors that can introduce access control weaknesses:
Potential Mitigations
- Compartmentalize the system to have “safe” areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
- Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
Related Attack Patterns
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- https://cwe.mitre.org/data/definitions/564.html
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