Out-of-bounds read and write vulnerabilities represent critical security vulnerabilities that occur when software accesses memory locations beyond the allocated boundaries of data structures such as arrays, buffers, or other memory regions.

These vulnerabilities can lead to information disclosure, system crashes, and in severe cases, arbitrary code execution that allows attackers to gain unauthorized control over affected systems.

Understanding these vulnerabilities is essential for developers, security professionals, and system administrators as they remain among the most prevalent and dangerous security issues in modern software applications.

Out-of-Bounds Read Vulnerability

Out-of-bounds read vulnerabilities occur when a program attempts to read data from memory locations that extend beyond the allocated boundaries of a buffer or array.

This type of vulnerability can result in the disclosure of sensitive information stored in adjacent memory locations, potentially exposing passwords, cryptographic keys, or other confidential data that should remain protected.

The fundamental cause of out-of-bounds read vulnerabilities lies in insufficient bounds checking during memory access operations. When developers fail to validate array indices or buffer sizes properly, programs may inadvertently access memory regions that contain unintended data.

This becomes particularly problematic in languages like C and C++ that provide direct memory management capabilities without built-in bounds checking mechanisms.

Consider the following vulnerable code example:

cchar buffer[10];
char user_input[20];
int index;

// Vulnerable code – no bounds checking
printf(“Data: %cn”, buffer[index]);

In this scenario, if the index value exceeds the buffer’s allocated size of 10 elements, the program will read from memory locations beyond the intended boundary.

This can expose data from other variables, stack frames, or heap structures, creating opportunities for information leakage attacks.

The Heartbleed vulnerability (CVE-2014-0160) serves as a prominent real-world example of an out-of-bounds read vulnerability. This vulnerability in OpenSSL allowed attackers to read up to 64KB of memory from vulnerable servers by sending malformed heartbeat requests that specified larger payload sizes than actually provided.

Attackers exploited this vulnerability to extract sensitive information, including private keys, passwords, and personal data, from millions of affected systems worldwide.

Out-of-Bounds Write Vulnerability

Out-of-bounds write vulnerabilities, commonly known as buffer overflow attacks, occur when programs write data beyond the allocated boundaries of memory buffers.

These vulnerabilities are particularly dangerous because they can overwrite critical program data, function return addresses, or other executable code, potentially leading to arbitrary code execution and complete system compromise.

Buffer overflow vulnerabilities typically manifest in two primary forms: stack-based and heap-based overflows. Stack-based overflows occur when local variables or function parameters are overwritten on the program stack, while heap-based overflows target dynamically allocated memory regions. Both types can be exploited to hijack program execution flow and execute malicious code.

The following code demonstrates a classic buffer overflow vulnerability:

cvoid vulnerable_function(char *input) {
char buffer[256];
strcpy(buffer, input); // No bounds checking
printf(“Buffer contents: %sn”, buffer);
}

When the input parameter contains more than 255 characters (plus null terminator), the strcpy function will write beyond the buffer’s boundaries, potentially overwriting return addresses, stack canaries, or other critical data structures. Skilled attackers can craft specific input payloads to redirect program execution to malicious code.

The Morris Worm of 1988 represents one of the earliest and most significant examples of buffer overflow exploitation. This self-replicating program exploited buffer overflow vulnerabilities in the fingerd daemon and sendmail program to propagate across UNIX systems connected to the early Internet, demonstrating the destructive potential of out-of-bounds write vulnerabilities.

How Out-of-Bounds Read & Write Vulnerability Occurs

Cause CategoryDescriptionCode Example/ScenarioVulnerability TypeCommon Languages AffectedInsufficient Input ValidationPrograms fail to verify that user-supplied data falls within expected ranges or buffer sizes before processingchar buffer; int index = user_input; return buffer[index]; – No validation of index valueBoth Read & WriteC, C++, AssemblyImproper Array IndexingUsing loop counters, user input, or calculated values as array indices without proper bounds checkingfor(int i = 0; i