Potential time of check time of use vulnerability (chmod)

Description

Usage of the `chmod` function call hints at a potential Time Of Check Time Of Use (TOCTOU) vulnerability. An attacker may be able to modify the file being specified by the `chmod` function prior to the `chmod` function being called. Since `chmod` will resolve symbolic links, an attacker may be able to exploit this fact to have files outside of their control modified. It is recommended that the `fchmod` function be used instead since this function takes a file descriptor instead of a file.

Examples

Insecure Code

chmod("example.txt", 0644);

Secure Code

int fd = open("example.txt", O_RDWR); fchmod(fd, 0644);

Remediation

Replace `chmod` with `fchmod` and ensure the opened file descriptor is pointing to the correct file or directory prior to executing `fchmod` or any other file-based operations.

Rule Details

Field	Value
ID	CODE-0607
Category	InsecureConfig
Severity	MEDIUM
CWE	CWE-362
Confidence	HIGH
Impact	MEDIUM
Likelihood	MEDIUM
Exploitability	MODERATE
Tags	TOCTOU, file permissions
OWASP	A5:2017-Broken Access Control, A01:2021-Broken Access Control

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