CWE-180 不正确的行为次序：规范化之前验证

Incorrect Behavior Order: Validate Before Canonicalize

结构: Simple

Abstraction: Base

状态: Draft

被利用可能性: unkown

基本描述

The software validates input before it is canonicalized, which prevents the software from detecting data that becomes invalid after the canonicalization step.

扩展描述

This can be used by an attacker to bypass the validation and launch attacks that expose weaknesses that would otherwise be prevented, such as injection.

适用平台

Language: {'cwe_Class': 'Language-Independent', 'cwe_Prevalence': 'Undetermined'}

常见的影响

范围	影响	注释
Access Control	Bypass Protection Mechanism

可能的缓解方案

MIT-20 Implementation

策略: Input Validation

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass whitelist validation schemes by introducing dangerous inputs after they have been checked.

示例代码

例

The following code attempts to validate a given input path by checking it against a whitelist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/".

bad Java

String path = getInputPath();
if (path.startsWith("/safe_dir/"))
{

File f = new File(path);
return f.getCanonicalPath();

}

The problem with the above code is that the validation step occurs before canonicalization occurs. An attacker could provide an input path of "/safe_dir/../" that would pass the validation step. However, the canonicalization process sees the double dot as a traversal to the parent directory and hence when canonicized the path would become just "/".

To avoid this problem, validation should occur after canonicalization takes place. In this case canonicalization occurs during the initialization of the File object. The code below fixes the issue.

good Java

String path = getInputPath();
File f = new File(path);
if (f.getCanonicalPath().startsWith("/safe_dir/"))
{

return f.getCanonicalPath();

}

分析过的案例

标识	说明	链接
CVE-2002-0433	Product allows remote attackers to view restricted files via an HTTP request containing a "*" (wildcard or asterisk) character.	https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2002-0433
CVE-2003-0332	Product modifies the first two letters of a filename extension after performing a security check, which allows remote attackers to bypass authentication via a filename with a .ats extension instead of a .hts extension.	https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2003-0332
CVE-2002-0802	Database consumes an extra character when processing a character that cannot be converted, which could remove an escape character from the query and make the application subject to SQL injection attacks.	https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2002-0802
CVE-2000-0191	Overlaps "fakechild/../realchild"	https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2000-0191
CVE-2004-2363	Product checks URI for "<" and other literal characters, but does it before hex decoding the URI, so "%3E" and other sequences are allowed.	https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-2363

Notes

分类映射

映射的分类名	ImNode ID	Fit	Mapped Node Name
PLOVER			Validate-Before-Canonicalize
OWASP Top Ten 2004	A1	CWE More Specific	Unvalidated Input
The CERT Oracle Secure Coding Standard for Java (2011)	IDS01-J	Exact	Normalize strings before validating them
SEI CERT Oracle Coding Standard for Java	IDS01-J	Exact	Normalize strings before validating them

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