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These file systems use a privileges and permissions model to protect file access. When a file is created, the file access permissions of the file immediately dictate who may access or operate on the file. When a program creates a file with insufficiently restrictive access permissions, an attacker may read or modify the file before the program can modify the permissions. Consequently, files must be created with access permissions that prevent unauthorized file access.
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In this noncompliant code example, the access permissions of any file created are implementation-defined and may fail to not prevent unauthorized access.
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Java 1.6 and earlier lack a mechanism for specifying default permissions upon file creation. Consequently, the problem must be avoided or solved using some mechanism external to Java, such as by using native code and the Java Native Interface (JNI).
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The Files.newByteChannel() method allows a file to be created with specific permissions. This method is platform-independent, but the actual permissions are platform-specific. The following This compliant solution shows defines sufficiently restrictive permissions for POSIX platforms.
| Code Block | ||
|---|---|---|
| ||
Path file = new File("file").toPath();
// Throw exception rather than overwrite existing file
Set<OpenOption> options = new HashSet<OpenOption>();
options.add(StandardOpenOption.CREATE_NEW);
options.add(StandardOpenOption.APPEND);
// File permissions should be such that only user may read/write file
Set<PosixFilePermission> perms =
PosixFilePermissions.fromString("rw-------");
FileAttribute<Set<PosixFilePermission>> attr =
PosixFilePermissions.asFileAttribute(perms);
try (SeekableByteChannel sbc =
Files.newByteChannel(file, options, attr)) {
// write data
};
|
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FIO01-EX0: When a file is created inside a directory that is both secure and unreadable by untrusted users, that file may be created with the default access permissions. See rule FIO00-J. Do not operate on files in shared directories for the definition of a secure directory. This could be the case if, for example, the entire file system is trusted or is accessible only to trusted users. See rule FIO00-J. for the definition of a secure directory.
FIO01-EX1: Files that do not contain sensitive privileged information need not be created with specific access permissions.
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Files created with insufficiently restrictive access permissions result in information disclosure, especially if the program creating the file populates the sensitive information. The ability to determine whether an existing file has been opened or a new file has been created provides greater assurance that only the intended file is acted upon.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
FIO01-J | medium | probable | high | P4 | L3 |
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="56b90fec80441cde-5c1f52cc-453d4492-929d8bcb-99edbc5b47b108b470ca3d37"><ac:plain-text-body><![CDATA[ | [ISO/IEC TR 24772:2010 | http://www.aitcnet.org/isai/] | Missing or Inconsistent Access Control [XZN] | ]]></ac:plain-text-body></ac:structured-macro> |
CWE-279. Incorrect execution-assigned permissions | ||||
| CWE-276. Incorrect default permissions | |||
| CWE-732. Incorrect permission assignment for critical resource |
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="9a2e3252c3fda8ee-5270a367-47824fa3-95709bbc-c8923052a1d878443e0c2c51"><ac:plain-text-body><![CDATA[ | [[API 2006 | AA. Bibliography#API 06]] |
| ]]></ac:plain-text-body></ac:structured-macro> |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="affe4dc69b081653-3e96ef9b-45ca4a2c-b7829c65-07b58c726f5d7799df4a1479"><ac:plain-text-body><![CDATA[ | [[CVE | AA. Bibliography#CVE]] |
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="1e7e641c7a78626f-5e65889f-46da43cd-bf379624-5ed6f8e443e40aa8969b49b4"><ac:plain-text-body><![CDATA[ | [[Dowd 2006 | AA. Bibliography#Dowd 06]] | Chapter 9, "UNIX 1: Privileges and Files" | ]]></ac:plain-text-body></ac:structured-macro> |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="bd7fdb89ba1125fb-b795b44f-439d4cd4-a1e2b498-f66c82832f5e8ba07171b7ff"><ac:plain-text-body><![CDATA[ | [[J2SE 2011 | AA. Bibliography#J2SE 11]] |
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="26ac61410a9cf644-f67c8339-4a6b493d-a066b7be-6ebd64a5de4766f214c1182f"><ac:plain-text-body><![CDATA[ | [[OpenBSD | AA. Bibliography#OpenBSD]] |
| ]]></ac:plain-text-body></ac:structured-macro> |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="438438e86a355349-774d83a3-48934df5-929cb6e8-364e4cb04042197880839653"><ac:plain-text-body><![CDATA[ | [[Open Group 2004 | AA. Bibliography#Open Group 04]] | "The | ]]></ac:plain-text-body></ac:structured-macro> |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="abbbb903299765e3-c6c6a687-4d8e43c0-b3d4aefd-bdfcf0aff832c18469b72ea8"><ac:plain-text-body><![CDATA[ | [[Viega 2003 | AA. Bibliography#Viega 03]] | Section 2.7, "Restricting Access Permissions for New Files on UNIX" | ]]></ac:plain-text-body></ac:structured-macro> |
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