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Access of Memory Location After End of Buffer

Incomplete Base
Structure: Simple
Description

This vulnerability occurs when software attempts to read from or write to a memory buffer using an index or pointer that points past the buffer's allocated boundary.

Extended Description

This flaw, often called a buffer over-read or over-write, happens when a program incorrectly calculates a memory position. It typically stems from a pointer being incremented too far, an index being miscalculated, or pointer arithmetic producing an invalid address that lands outside the intended buffer's range. The result is access to adjacent memory that doesn't belong to the buffer, which can corrupt data or expose sensitive information. For developers, this is a critical memory safety issue. It can lead to crashes, unpredictable behavior, or be exploited to leak confidential data or gain code execution. Common causes include off-by-one errors in loops, incorrect size calculations, or using untrusted input directly as an array index without proper bounds checking.
Common Consequences 3
Scope: Confidentiality

Impact: Read Memory

For an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffer's position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.

Scope: IntegrityAvailability

Impact: Modify MemoryDoS: Crash, Exit, or Restart

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.

Scope: Integrity

Impact: Modify MemoryExecute Unauthorized Code or Commands

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), they can redirect a function pointer to their 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.
Detection Methods 2
FuzzingHigh
Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.
Automated Static AnalysisHigh
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
Demonstrative Examples 4

ID : DX-1

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.

Code Example:

Bad
C
c

/*routine that ensures user_supplied_addr is in the right format for conversion /

c
This function allocates a buffer of 64 bytes to store the hostname, however there is no guarantee that the hostname will not be larger than 64 bytes. If an attacker specifies an address which resolves to a very large hostname, then the function may overwrite sensitive data or even relinquish control flow to the attacker.
Note that this example also contains an unchecked return value (Unchecked Return Value) that can lead to a NULL pointer dereference (NULL Pointer Dereference).

ID : DX-114

In the following example, it is possible to request that memcpy move a much larger segment of memory than assumed:

Code Example:

Bad
C
c

/* if chunk info is valid, return the size of usable memory,*

c
If returnChunkSize() happens to encounter an error it will return -1. Notice that the return value is not checked before the memcpy operation (Unchecked Return Value), so -1 can be passed as the size argument to memcpy() (Buffer Access with Incorrect Length Value). Because memcpy() assumes that the value is unsigned, it will be interpreted as MAXINT-1 (Signed to Unsigned Conversion Error), and therefore will copy far more memory than is likely available to the destination buffer (Out-of-bounds Write, Access of Memory Location After End of Buffer).
ID : DX-19
This example applies an encoding procedure to an input string and stores it into a buffer.
Code Example:
Bad
C
c


/* encode to < /
}
else dst_buf[dst_index++] = user_supplied_string[i];}
return dst_buf;}
The programmer attempts to encode the ampersand character in the user-controlled string, however the length of the string is validated before the encoding procedure is applied. Furthermore, the programmer assumes encoding expansion will only expand a given character by a factor of 4, while the encoding of the ampersand expands by 5. As a result, when the encoding procedure expands the string it is possible to overflow the destination buffer if the attacker provides a string of many ampersands.
ID : DX-91
In the following C/C++ example the method processMessageFromSocket() will get a message from a socket, placed into a buffer, and will parse the contents of the buffer into a structure that contains the message length and the message body. A for loop is used to copy the message body into a local character string which will be passed to another method for processing.
Code Example:
Bad
C
c


// get message from socket and store into buffer*


c


c


// process message*
success = processMessage(message);}
return success;}
However, the message length variable (msgLength) from the structure is used as the condition for ending the for loop without validating that msgLength accurately reflects the actual length of the message body (Unchecked Input for Loop Condition). If msgLength indicates a length that is longer than the size of a message body (Improper Handling of Length Parameter Inconsistency), then this can result in a buffer over-read by reading past the end of the buffer (Buffer Over-read).
  
Observed Examples 6
CVE-2009-2550Classic stack-based buffer overflow in media player using a long entry in a playlist
CVE-2009-2403Heap-based buffer overflow in media player using a long entry in a playlist
CVE-2009-0689large precision value in a format string triggers overflow
CVE-2009-0558attacker-controlled array index leads to code execution
CVE-2008-4113OS kernel trusts userland-supplied length value, allowing reading of sensitive information
CVE-2007-4268Chain: integer signedness error (Signed to Unsigned Conversion Error) passes signed comparison, leading to heap overflow (Heap-based Buffer Overflow)
  
References 1
Automated Source Code Reliability Measure (ASCRM)
Object Management Group (OMG)
01-2016
http://www.omg.org/spec/ASCRM/1.0/
ID: REF-961
 
  
    
 
 
Applicable Platforms 
 
 
 
 
 
Languages:
 
 
 C : OftenC++ : Often 
  
  
 
 
 
        
 
 
Functional Areas 
 
 
 
     
  1. Memory Management
    2.  
 
 
  
 
 
Affected Resources 
 
 
 
     
  1. Memory
    2.  
 
 
  
 
 
Related Weaknesses 
 
 
 
 
  ChildOf:
 Improper Restriction of Operations within the Bounds of a Memory Buffer (CWE-119) 
  ChildOf:
 Improper Restriction of Operations within the Bounds of a Memory Buffer (CWE-119) 
  ChildOf:
 Improper Restriction of Operations within the Bounds of a Memory Buffer (CWE-119) 
 
 
 
 
Taxonomy Mapping 
  • OMG ASCRM