CWE-179 不正确的行为次序：过早验证

Incorrect Behavior Order: Early Validation

结构: Simple

Abstraction: Base

状态: Incomplete

被利用可能性: unkown

基本描述

The software validates input before applying protection mechanisms that modify the input, which could allow an attacker to bypass the validation via dangerous inputs that only arise after the modification.

扩展描述

Software needs to validate data at the proper time, after data has been canonicalized and cleansed. Early validation is susceptible to various manipulations that result in dangerous inputs that are produced by canonicalization and cleansing.

相关缺陷

  • cwe_Nature: ChildOf cwe_CWE_ID: 20 cwe_View_ID: 699 cwe_Ordinal: Primary

  • cwe_Nature: ChildOf cwe_CWE_ID: 693 cwe_View_ID: 1000

  • cwe_Nature: ChildOf cwe_CWE_ID: 696 cwe_View_ID: 1000 cwe_Ordinal: Primary

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', 'Integrity'] ['Bypass Protection Mechanism', 'Execute Unauthorized Code or Commands'] An attacker could include dangerous input that bypasses validation protection mechanisms which can be used to launch various attacks including injection attacks, execute arbitrary code or cause other unintended behavior.

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();
}

例

This script creates a subdirectory within a user directory and sets the user as the owner.

bad PHP

function createDir($userName,$dirName){
$userDir = '/users/'. $userName;
if(strpos($dirName,'..') !== false){
echo 'Directory name contains invalid sequence';
return;
}
//filter out '~' because other scripts identify user directories by this prefix
$dirName = str_replace('~','',$dirName);
$newDir = $userDir . $dirName;
mkdir($newDir, 0700);
chown($newDir,$userName);
}

While the script attempts to screen for '..' sequences, an attacker can submit a directory path including ".~.", which will then become ".." after the filtering step. This allows a Path Traversal (CWE-21) attack to occur.

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
CVE-2002-0934 Directory traversal vulnerability allows remote attackers to read or modify arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2002-0934
CVE-2003-0282 Directory traversal vulnerability allows attackers to overwrite arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2003-0282

Notes

分类映射

映射的分类名 ImNode ID Fit Mapped Node Name
PLOVER Early Validation Errors

相关攻击模式

  • CAPEC-3
  • CAPEC-43
  • CAPEC-71

引用