SEI CERT C Coding Standard

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On POSIX-compliant systems, the permissions may be restricted by the value of the POSIX umask() function [Open Group 2004IEEE Std 1003.1:2013].

The operating system modifies the access permissions by computing the intersection of the inverse of the umask and the permissions requested by the process [Viega 2003]. For example, if the variable requested_permissions contained the permissions passed to the operating system to create a new file, the variable actual_permissions would be the actual permissions that the operating system would use to create the file:

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Creating files with weak access permissions may allow unintended access to those files.

Recommendation

Severity

Likelihood

Remediation Cost

Priority

Level

FIO06-C

Medium

Probable

High

P4

L3

Automated Detection

Tool

Version

Checker

Description

PRQA QA-C
CodeSonar
Include Page
PRQA
CodeSonar_V
PRQA
CodeSonar_V
warncall fopenPartially implemented
(customization)

CodeSonar's custom checking infrastructure allows users to implement checks such as the following.

  • A check for all uses of fopen().
  • A check for calls to open() with only two arguments.
  • A check for calls to open() where the third argument does not satisfy some specified requirement.
Helix QAC

Include Page
Helix QAC_V
Helix QAC_V

C5013
LDRA tool suite
Include Page
LDRA_V
LDRA_V
44 SEnhanced Enforcement

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

SEI CERT C++
Secure
Coding StandardVOID FIO06-CPP. Create files with appropriate access permissions
CERT Oracle Secure Coding Standard for JavaFIO01-J. Create files with appropriate access permissions
ISO/IEC TR 24772:2013Missing or Inconsistent Access Control [XZN]
MITRE CWECWE-276, Insecure default permissions
CWE-279, Insecure execution-assigned permissions
CWE-732, Incorrect permission assignment for critical resource

Bibliography

[CVE]
 

[Dowd 2006]Chapter 9, "UNIX 1: Privileges and Files"
[IEEE Std 1003.1:2013]XSH, System Interfaces, open
XSH, System Interfaces, umask
[ISO/IEC 9899:2011]Subclause K.3.5.2.1, "The fopen_s Function"
[OpenBSD]
 "The open Function"
"The umask Function"[

[
Open Group 2004]
Viega 2003]Section 2.7, "Restricting Access Permissions for New Files on UNIX"

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