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CWE
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Improper Restriction of Operations within the Bounds of a Memory Buffer

ID: 119Date: (C)2012-05-14   (M)2017-10-17
Type: weaknessStatus: USABLE
Abstraction Type: Class





Description

The software performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.

Extended Description

Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced. This can cause read or write operations to be performed on memory locations that may be associated with other variables, data structures, or internal program data.

As a result, an attacker may be able to execute arbitrary code, alter the intended control flow, read sensitive information, or cause the system to crash.

Likelihood of Exploit: High

Applicable Platforms
Language: Often
Language: C
Language: Often
Language: C++
Language: Assembly
Language Class: Languages without memory management support

Time Of Introduction

  • Architecture and Design
  • Implementation
  • Operation

Related Attack Patterns

Common Consequences

ScopeTechnical ImpactNotes
Integrity
Confidentiality
Availability
 
Execute unauthorized code or commands
Modify memory
 
If the memory accessible by the attacker can be effectively controlled, it may be possible to execute arbitrary code, as with a standard buffer overflow.
If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), he can redirect a function pointer to his own malicious code. Even when the attacker can only modify a single byte arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data -- such as a flag indicating whether the user is an administrator.
 
Availability
Confidentiality
 
Read memory
DoS: crash / exit / restart
DoS: resource consumption (CPU)
DoS: resource consumption (memory)
 
Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
 
Confidentiality
 
Read memory
 
In the case of an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffers position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.
 

Detection Methods

NameDescriptionEffectivenessNotes
Automated Static Analysis
 
This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.
Automated static analysis generally does not account for environmental considerations when reporting out-of-bounds memory operations. This can make it difficult for users to determine which warnings should be investigated first. For example, an analysis tool might report buffer overflows that originate from command line arguments in a program that is not expected to run with setuid or other special privileges.
 
High
 
 
Automated Dynamic Analysis
 
This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
 
  

Potential Mitigations

PhaseStrategyDescriptionEffectivenessNotes
Requirements
 
Language Selection
 
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.
Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
 
  
Architecture and Design
 
Libraries or Frameworks
 
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Examples include the Safe C String Library (SafeStr) by Messier and Viega [R.119.3], and the Strsafe.h library from Microsoft [R.119.2]. These libraries provide safer versions of overflow-prone string-handling functions.
 
 This is not a complete solution, since many buffer overflows are not related to strings.
 
Build and Compilation
 
Compilation or Build Hardening
 
Run or compile the software using features or extensions that automatically provide a protection mechanism that mitigates or eliminates buffer overflows.
For example, certain compilers and extensions provide automatic buffer overflow detection mechanisms that are built into the compiled code. Examples include the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice.
 
Defense in Depth
 
This is not necessarily a complete solution, since these mechanisms can only detect certain types of overflows. In addition, an attack could still cause a denial of service, since the typical response is to exit the application.
 
Implementation
 
 Consider adhering to the following rules when allocating and managing an application's memory:

 
  
Operation
 
Environment Hardening
 
Use a feature like Address Space Layout Randomization (ASLR) [R.119.4] [R.119.6].
 
Defense in Depth
 
This is not a complete solution. However, it forces the attacker to guess an unknown value that changes every program execution. In addition, an attack could still cause a denial of service, since the typical response is to exit the application.
 
Operation
 
Environment Hardening
 
Use a CPU and operating system that offers Data Execution Protection (NX) or its equivalent [R.119.6] [R.119.7].
 
Defense in Depth
 
This is not a complete solution, since buffer overflows could be used to overwrite nearby variables to modify the software's state in dangerous ways. In addition, it cannot be used in cases in which self-modifying code is required. Finally, an attack could still cause a denial of service, since the typical response is to exit the application.
 
Implementation
 
 Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.
 
Moderate
 
This approach is still susceptible to calculation errors, including issues such as off-by-one errors (CWE-193) and incorrectly calculating buffer lengths (CWE-131).
 

Relationships

Related CWETypeViewChain
CWE-119 ChildOf CWE-890 Category CWE-888  

Demonstrative Examples   (Details)

  1. In the following code, the method retrieves a value from an array at a specific array index location that is given as an input parameter to the method (Demonstrative Example Id DX-100)
  2. The following example asks a user for an offset into an array to select an item. (Demonstrative Example Id DX-90)
  3. This example applies an encoding procedure to an input string and stores it into a buffer. (Demonstrative Example Id DX-19)
  4. This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer. (Demonstrative Example Id DX-1)

Observed Examples

  1. CVE-2009-2550 : Classic stack-based buffer overflow in media player using a long entry in a playlist
  2. CVE-2009-2403 : Heap-based buffer overflow in media player using a long entry in a playlist
  3. CVE-2009-0689 : large precision value in a format string triggers overflow
  4. CVE-2009-0690 : negative offset value leads to out-of-bounds read
  5. CVE-2009-1532 : malformed inputs cause accesses of uninitialized or previously-deleted objects, leading to memory corruption
  6. CVE-2009-1528 : chain: lack of synchronization leads to memory corruption
  7. CVE-2009-0558 : attacker-controlled array index leads to code execution
  8. CVE-2009-0269 : chain: -1 value from a function call was intended to indicate an error, but is used as an array index instead.
  9. CVE-2009-0566 : chain: incorrect calculations lead to incorrect pointer dereference and memory corruption
  10. CVE-2009-1350 : product accepts crafted messages that lead to a dereference of an arbitrary pointer
  11. CVE-2009-0191 : chain: malformed input causes dereference of uninitialized memory
  12. CVE-2008-4113 : OS kernel trusts userland-supplied length value, allowing reading of sensitive information

For more examples, refer to CVE relations in the bottom box.

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

TaxynomyIdNameFit
OWASP Top Ten 2004 A5
 
Buffer Overflows
 
Exact
 
CERT C Secure Coding ARR00-C
 
Understand how arrays work
 
 
CERT C Secure Coding ARR33-C
 
Guarantee that copies are made into storage of sufficient size
 
 
CERT C Secure Coding ARR34-C
 
Ensure that array types in expressions are compatible
 
 
CERT C Secure Coding ARR35-C
 
Do not allow loops to iterate beyond the end of an array
 
 
CERT C Secure Coding ENV01-C
 
Do not make assumptions about the size of an environment variable
 
 
CERT C Secure Coding FIO37-C
 
Do not assume character data has been read
 
 
CERT C Secure Coding MEM09-C
 
Do not assume memory allocation routines initialize memory
 
 
CERT C Secure Coding STR31-C
 
Guarantee that storage for strings has sufficient space for character data and the null terminator
 
 
CERT C Secure Coding STR32-C
 
Null-terminate byte strings as required
 
 
CERT C Secure Coding STR33-C
 
Size wide character strings correctly
 
 
WASC 7
 
Buffer Overflow
 
 
CERT C++ Secure Coding ARR00-CPP
 
Understand when to prefer vectors over arrays
 
 
CERT C++ Secure Coding ARR30-CPP
 
Guarantee that array and vector indices are within the valid range
 
 
CERT C++ Secure Coding ARR33-CPP
 
Guarantee that copies are made into storage of sufficient size
 
 
CERT C++ Secure Coding ARR35-CPP
 
Do not allow loops to iterate beyond the end of an array or container
 
 
CERT C++ Secure Coding STR31-CPP
 
Guarantee that storage for character arrays has sufficient space for character data and the null terminator
 
 
CERT C++ Secure Coding STR32-CPP
 
Null-terminate character arrays as required
 
 
CERT C++ Secure Coding MEM09-CPP
 
Do not assume memory allocation routines initialize memory
 
 
CERT C++ Secure Coding FIO37-CPP
 
Do not assume character data has been read
 
 
CERT C++ Secure Coding ENV01-CPP
 
Do not make assumptions about the size of an environment variable
 
 

References:

  1. M. Howard D. LeBlanc .Writing Secure Code 2nd Edition. Microsoft. Section:'Chapter 5, "Public Enemy #1: The Buffer Overrun" Page 127; Chapter 14, "Prevent I18N Buffer Overruns" Page 441'. Published on 2002.
  2. Microsoft .Using the Strsafe.h Functions.
  3. Matt Messier John Viega .Safe C String Library v1.0.3.
  4. Michael Howard .Address Space Layout Randomization in Windows Vista.
  5. Arjan van de Ven .Limiting buffer overflows with ExecShield.
  6. .PaX.
  7. Microsoft .Understanding DEP as a mitigation technology part 1.
  8. Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 5, "Memory Corruption", Page 167.'. Published on 2006.
  9. Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 5, "Protection Mechanisms", Page 189.'. Published on 2006.
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