계: Input Validation and Representation

입력 검증 및 표현 문제는 메타 문자, 대체 인코딩 및 숫자 표현 때문에 발생합니다. 보안 문제는 입력을 신뢰하기 때문에 발생합니다. 문제로는 "Buffer Overflows", "Cross-Site Scripting" 공격, "SQL Injection", 그 외 여러 가지가 있습니다.

XML Entity Expansion Injection

Abstract

DTD(문서 유형 정의) 항목 확인을 차단하거나 제한하도록 구성되지 않은 XML 파서를 사용하면 파서가 XML Entity Expansion Injection에 노출될 수 있습니다.

Explanation

XML Bombs라고도 하는 XML Entity Expansion Injection은 서버의 할당된 리소스를 모두 소진할 때까지 기하급수적으로 확장하고 올바른 형식의 XML 블록을 이용하는 DoS 공격입니다. XML을 사용하면 문자열 대체 매크로 역할을 하는 사용자 지정 항목을 정의할 수 있습니다. 공격자는 반복적인 항목 확인을 중첩하여 서버 리소스를 손쉽게 중단시킬 수 있습니다.

다음 XML 문서는 XML Bomb의 예를 보여줍니다.


    <?xml version="1.0"?>
    <!DOCTYPE lolz [
      <!ENTITY lol "lol">
      <!ENTITY lol2 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
      <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">
      <!ENTITY lol4 "&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;">
      <!ENTITY lol5 "&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;">
      <!ENTITY lol6 "&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;">
      <!ENTITY lol7 "&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;">
      <!ENTITY lol8 "&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;">
      <!ENTITY lol9 "&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;">
    ]>
    <lolz>&lol9;</lolz>

이 테스트는 작은 XML 문서를 3 GB 이상의 메모리로 확장하여 서버를 중단시킬 수 있습니다.

References

[1] XML External Entity (XXE) Processing OWASP

[2] Testing for XML Injection OWASP

[3] XML External Entities The Web Application Security Consortium

[4] Standards Mapping - Common Weakness Enumeration CWE ID 776

[5] Standards Mapping - Common Weakness Enumeration Top 25 2024 [24] CWE ID 400

[6] Standards Mapping - DISA Control Correlation Identifier Version 2 CCI-001094, CCI-001310, CCI-002385

[7] Standards Mapping - NIST Special Publication 800-53 Revision 4 SC-5 Denial of Service Protection (P1), SI-10 Information Input Validation (P1)

[8] Standards Mapping - NIST Special Publication 800-53 Revision 5 SC-5 Denial of Service Protection, SI-10 Information Input Validation

[9] Standards Mapping - OWASP API 2023 API4 Unrestricted Resource Consumption

[10] Standards Mapping - OWASP Application Security Verification Standard 4.0 12.1.2 File Upload Requirements (L2 L3)

[11] Standards Mapping - OWASP Mobile 2014 M1 Weak Server Side Controls

[12] Standards Mapping - OWASP Mobile 2024 M4 Insufficient Input/Output Validation

[13] Standards Mapping - OWASP Mobile Application Security Verification Standard 2.0 MASVS-CODE-4

[14] Standards Mapping - OWASP Top 10 2004 A9 Application Denial of Service

[15] Standards Mapping - OWASP Top 10 2007 A2 Injection Flaws

[16] Standards Mapping - OWASP Top 10 2010 A1 Injection

[17] Standards Mapping - OWASP Top 10 2013 A1 Injection

[18] Standards Mapping - OWASP Top 10 2017 A4 XML External Entities (XXE)

[19] Standards Mapping - OWASP Top 10 2021 A05 Security Misconfiguration

[20] Standards Mapping - Payment Card Industry Data Security Standard Version 1.1 Requirement 6.5.9

[21] Standards Mapping - Payment Card Industry Data Security Standard Version 3.0 Requirement 6.5.1

[22] Standards Mapping - Payment Card Industry Data Security Standard Version 3.1 Requirement 6.5.1

[23] Standards Mapping - Payment Card Industry Data Security Standard Version 3.2 Requirement 6.5.1

[24] Standards Mapping - Payment Card Industry Data Security Standard Version 3.2.1 Requirement 6.5.1

[25] Standards Mapping - Payment Card Industry Data Security Standard Version 4.0 Requirement 6.2.4

[26] Standards Mapping - Payment Card Industry Data Security Standard Version 4.0.1 Requirement 6.2.4

[27] Standards Mapping - Payment Card Industry Software Security Framework 1.0 Control Objective 4.2 - Critical Asset Protection

[28] Standards Mapping - Payment Card Industry Software Security Framework 1.1 Control Objective 4.2 - Critical Asset Protection, Control Objective B.3.1 - Terminal Software Attack Mitigation, Control Objective B.3.1.1 - Terminal Software Attack Mitigation

[29] Standards Mapping - Payment Card Industry Software Security Framework 1.2 Control Objective 4.2 - Critical Asset Protection, Control Objective B.3.1 - Terminal Software Attack Mitigation, Control Objective B.3.1.1 - Terminal Software Attack Mitigation, Control Objective C.3.2.2 - Web Software Attack Mitigation

[30] Standards Mapping - Security Technical Implementation Guide Version 3.1 APP6080 CAT II

[31] Standards Mapping - Security Technical Implementation Guide Version 3.4 APP6080 CAT II

[32] Standards Mapping - Security Technical Implementation Guide Version 3.5 APP6080 CAT II

[33] Standards Mapping - Security Technical Implementation Guide Version 3.6 APP6080 CAT II

[34] Standards Mapping - Security Technical Implementation Guide Version 3.7 APP6080 CAT II

[35] Standards Mapping - Security Technical Implementation Guide Version 3.9 APP6080 CAT II

[36] Standards Mapping - Security Technical Implementation Guide Version 3.10 APP6080 CAT II

[37] Standards Mapping - Security Technical Implementation Guide Version 4.2 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[38] Standards Mapping - Security Technical Implementation Guide Version 4.3 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[39] Standards Mapping - Security Technical Implementation Guide Version 4.4 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[40] Standards Mapping - Security Technical Implementation Guide Version 4.5 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[41] Standards Mapping - Security Technical Implementation Guide Version 4.6 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[42] Standards Mapping - Security Technical Implementation Guide Version 4.7 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[43] Standards Mapping - Security Technical Implementation Guide Version 4.8 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[44] Standards Mapping - Security Technical Implementation Guide Version 4.9 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[45] Standards Mapping - Security Technical Implementation Guide Version 4.10 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[46] Standards Mapping - Security Technical Implementation Guide Version 4.11 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[47] Standards Mapping - Security Technical Implementation Guide Version 4.1 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[48] Standards Mapping - Security Technical Implementation Guide Version 5.1 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[49] Standards Mapping - Security Technical Implementation Guide Version 5.2 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[50] Standards Mapping - Security Technical Implementation Guide Version 5.3 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002530 CAT II, APSC-DV-002550 CAT I

[51] Standards Mapping - Security Technical Implementation Guide Version 6.1 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002530 CAT II, APSC-DV-002550 CAT I

[52] Standards Mapping - Web Application Security Consortium Version 2.00 XML Entity Expansion (WASC-44)

[53] Standards Mapping - Web Application Security Consortium 24 + 2 Denial of Service

desc.dataflow.abap.xml_entity_expansion_injection

Abstract

DTD(문서 유형 정의) 항목 확인을 차단하거나 제한하도록 구성되지 않은 XML 파서를 사용하면 파서가 XML Entity Expansion Injection에 노출될 수 있습니다.

Explanation

XML 엔터티 확장 injection 공격은 서버의 할당된 리소스를 모두 소모할 때까지 기하급수적으로 확장되는, 올바른 형식의 유효한 XML 블록을 이용하는 DoS 공격입니다. XML을 사용하면 문자열 대체 매크로로 작동하는 사용자 지정 엔터티를 정의할 수 있습니다. 되풀이되는 엔터티 확인을 중첩시켜 공격자가 서버 리소스를 쉽게 중단시킬 수 있습니다.

다음 XML 문서에서는 XML 폭탄의 예를 보여 줍니다.


<?xml version="1.0"?>
<!DOCTYPE lolz [
  <!ENTITY lol "lol">
  <!ENTITY lol2 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
  <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">
  <!ENTITY lol4 "&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;">
  <!ENTITY lol5 "&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;">
  <!ENTITY lol6 "&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;">
  <!ENTITY lol7 "&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;">
  <!ENTITY lol8 "&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;">
  <!ENTITY lol9 "&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;">
]>
<lolz>&lol9;</lolz>

이 테스트는 작은 XML 문서를 메모리에서 3GB 이상으로 확장시켜 서버를 중단시킬 수 있습니다.

References

[1] XML Denial of Service Attacks and Defenses MSDN Magazine

[2] XML External Entity (XXE) Processing OWASP

[3] Testing for XML Injection OWASP

[4] XML External Entities The Web Application Security Consortium

[5] Standards Mapping - Common Weakness Enumeration CWE ID 776

[6] Standards Mapping - Common Weakness Enumeration Top 25 2024 [24] CWE ID 400

[7] Standards Mapping - DISA Control Correlation Identifier Version 2 CCI-001094, CCI-001310, CCI-002385

[8] Standards Mapping - NIST Special Publication 800-53 Revision 4 SC-5 Denial of Service Protection (P1), SI-10 Information Input Validation (P1)

[9] Standards Mapping - NIST Special Publication 800-53 Revision 5 SC-5 Denial of Service Protection, SI-10 Information Input Validation

[10] Standards Mapping - OWASP API 2023 API4 Unrestricted Resource Consumption

[11] Standards Mapping - OWASP Application Security Verification Standard 4.0 12.1.2 File Upload Requirements (L2 L3)

[12] Standards Mapping - OWASP Mobile 2014 M1 Weak Server Side Controls

[13] Standards Mapping - OWASP Mobile 2024 M4 Insufficient Input/Output Validation

[14] Standards Mapping - OWASP Mobile Application Security Verification Standard 2.0 MASVS-CODE-4

[15] Standards Mapping - OWASP Top 10 2004 A9 Application Denial of Service

[16] Standards Mapping - OWASP Top 10 2007 A2 Injection Flaws

[17] Standards Mapping - OWASP Top 10 2010 A1 Injection

[18] Standards Mapping - OWASP Top 10 2013 A1 Injection

[19] Standards Mapping - OWASP Top 10 2017 A4 XML External Entities (XXE)

[20] Standards Mapping - OWASP Top 10 2021 A05 Security Misconfiguration

[21] Standards Mapping - Payment Card Industry Data Security Standard Version 1.1 Requirement 6.5.9

[22] Standards Mapping - Payment Card Industry Data Security Standard Version 3.0 Requirement 6.5.1

[23] Standards Mapping - Payment Card Industry Data Security Standard Version 3.1 Requirement 6.5.1

[24] Standards Mapping - Payment Card Industry Data Security Standard Version 3.2 Requirement 6.5.1

[25] Standards Mapping - Payment Card Industry Data Security Standard Version 3.2.1 Requirement 6.5.1

[26] Standards Mapping - Payment Card Industry Data Security Standard Version 4.0 Requirement 6.2.4

[27] Standards Mapping - Payment Card Industry Data Security Standard Version 4.0.1 Requirement 6.2.4

[28] Standards Mapping - Payment Card Industry Software Security Framework 1.0 Control Objective 4.2 - Critical Asset Protection

[29] Standards Mapping - Payment Card Industry Software Security Framework 1.1 Control Objective 4.2 - Critical Asset Protection, Control Objective B.3.1 - Terminal Software Attack Mitigation, Control Objective B.3.1.1 - Terminal Software Attack Mitigation

[30] Standards Mapping - Payment Card Industry Software Security Framework 1.2 Control Objective 4.2 - Critical Asset Protection, Control Objective B.3.1 - Terminal Software Attack Mitigation, Control Objective B.3.1.1 - Terminal Software Attack Mitigation, Control Objective C.3.2.2 - Web Software Attack Mitigation

[31] Standards Mapping - Security Technical Implementation Guide Version 3.1 APP6080 CAT II

[32] Standards Mapping - Security Technical Implementation Guide Version 3.4 APP6080 CAT II

[33] Standards Mapping - Security Technical Implementation Guide Version 3.5 APP6080 CAT II

[34] Standards Mapping - Security Technical Implementation Guide Version 3.6 APP6080 CAT II

[35] Standards Mapping - Security Technical Implementation Guide Version 3.7 APP6080 CAT II

[36] Standards Mapping - Security Technical Implementation Guide Version 3.9 APP6080 CAT II

[37] Standards Mapping - Security Technical Implementation Guide Version 3.10 APP6080 CAT II

[38] Standards Mapping - Security Technical Implementation Guide Version 4.2 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[39] Standards Mapping - Security Technical Implementation Guide Version 4.3 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[40] Standards Mapping - Security Technical Implementation Guide Version 4.4 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[41] Standards Mapping - Security Technical Implementation Guide Version 4.5 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[42] Standards Mapping - Security Technical Implementation Guide Version 4.6 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[43] Standards Mapping - Security Technical Implementation Guide Version 4.7 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[44] Standards Mapping - Security Technical Implementation Guide Version 4.8 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[45] Standards Mapping - Security Technical Implementation Guide Version 4.9 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[46] Standards Mapping - Security Technical Implementation Guide Version 4.10 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[47] Standards Mapping - Security Technical Implementation Guide Version 4.11 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[48] Standards Mapping - Security Technical Implementation Guide Version 4.1 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[49] Standards Mapping - Security Technical Implementation Guide Version 5.1 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[50] Standards Mapping - Security Technical Implementation Guide Version 5.2 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002550 CAT I

[51] Standards Mapping - Security Technical Implementation Guide Version 5.3 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002530 CAT II, APSC-DV-002550 CAT I

[52] Standards Mapping - Security Technical Implementation Guide Version 6.1 APSC-DV-002390 CAT II, APSC-DV-002400 CAT II, APSC-DV-002530 CAT II, APSC-DV-002550 CAT I

[53] Standards Mapping - Web Application Security Consortium Version 2.00 XML Entity Expansion (WASC-44)

[54] Standards Mapping - Web Application Security Consortium 24 + 2 Denial of Service

desc.controlflow.dotnet.xml_entity_expansion_injection

Abstract

DTD(문서 유형 정의) 항목 확인을 차단하거나 제한하도록 구성되지 않은 XML 파서를 사용하면 파서가 XML Entity Expansion Injection에 노출될 수 있습니다.

Explanation

XML Bombs라고 하는 XML Entity Expansion injection은 서버의 할당된 리소스를 모두 소모할 때까지 기하급수적으로 확장되는 올바른 형식의 유효한 XML 블록을 이용하는 DoS(Denial Of Service) 공격입니다. XML을 사용하면 문자열 대체 매크로로 작동하는 사용자 지정 엔터티를 정의할 수 있습니다. 되풀이되는 엔터티 확인을 중첩시켜 공격자가 서버 리소스를 쉽게 중단시킬 수 있습니다.

다음 XML 문서에서는 XML 폭탄의 예를 보여 줍니다.


<?xml version="1.0"?>
<!DOCTYPE lolz [
  <!ENTITY lol "lol">
  <!ENTITY lol2 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
  <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">
  <!ENTITY lol4 "&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;">
  <!ENTITY lol5 "&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;">
  <!ENTITY lol6 "&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;">
  <!ENTITY lol7 "&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;">
  <!ENTITY lol8 "&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;">
  <!ENTITY lol9 "&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;">
]>
<lolz>&lol9;</lolz>

이 테스트는 작은 XML 문서를 메모리에서 3GB 이상으로 확장시켜 서버를 중단시킬 수 있습니다.

References

[1] XML External Entity (XXE) Processing OWASP

[2] Testing for XML Injection OWASP

[3] XML External Entities The Web Application Security Consortium

[4] INJECT-5: Restrict XML inclusion Oracle