CWE-188: Reliance on Data/Memory Layout

What is Reliance on Data/Memory Layout?

• Overview: Reliance on Data/Memory Layout (CWE-188) occurs when software assumes a specific organization of data or memory, which can lead to unintended behavior when the memory layout changes, such as during platform transitions or protocol updates.

• Exploitation Methods:

• Attackers can manipulate or predict memory layouts to alter program behavior or access unintended data fields.
• Common attack patterns include exploiting assumptions about variable order, alignment, and padding to execute code or access restricted data.

• Security Impact:

• Direct consequences include incorrect program execution, data corruption, or crashes.
• Potential cascading effects involve unauthorized data access or privilege escalation due to misinterpreted data.
• Business impact may involve data breaches, lost customer trust, and regulatory non-compliance.

• Prevention Guidelines:

• Specific code-level fixes include avoiding assumptions about data layout and using standardized data structures.
• Security best practices involve validating all inputs, using abstraction layers, and avoiding direct memory manipulation.
• Recommended tools and frameworks include static analysis tools to detect layout dependencies and compilers with strict alignment checks.

Corgea can automatically detect and fix Reliance on Data/Memory Layout in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Low

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

// This code assumes a specific memory layout for struct Packet, which can lead to undefined behavior
#include <stdio.h>

struct Packet {
    unsigned short header;
    char payload[10];
    unsigned short footer;
};

void processPacket(char *buffer) {
    // Vulnerable: Assumes struct Packet memory layout is packed, which is compiler-specific
    struct Packet *pkt = (struct Packet *)buffer;  // This assumes no padding is added by the compiler
    printf("Header: %u\n", pkt->header);
    printf("Payload: %.10s\n", pkt->payload);
    printf("Footer: %u\n", pkt->footer);
}

int main() {
    char buffer[14] = {0x01, 0x00, 'H', 'e', 'l', 'l', 'o', 0, 0, 0, 0x02, 0x00};
    processPacket(buffer);
    return 0;
}

How to fix Reliance on Data/Memory Layout?

The vulnerability arises from assuming that a struct's memory layout will be consistent across different compilers and architectures. Compilers may add padding between struct members to align them in memory, which can lead to undefined behavior if we rely on a specific layout.

To fix this, we should avoid casting raw buffers to struct pointers. Instead, manually parse the buffer to extract the fields, respecting any alignment or padding that may exist. This ensures that the code is portable and behaves consistently across different environments.

Fixed Code Example

#include <stdio.h>

struct Packet {
    unsigned short header;
    char payload[10];
    unsigned short footer;
};

void processPacket(char *buffer) {
    // Fixed: Manually parse the buffer without assuming struct memory layout
    unsigned short header = *(unsigned short *)buffer;  // Extract header directly from buffer
    char payload[10];
    for (int i = 0; i < 10; ++i) {
        payload[i] = buffer[2 + i];  // Copy payload from buffer
    }
    unsigned short footer = *(unsigned short *)(buffer + 12);  // Extract footer directly from buffer

    printf("Header: %u\n", header);
    printf("Payload: %.10s\n", payload);
    printf("Footer: %u\n", footer);
}

int main() {
    char buffer[14] = {0x01, 0x00, 'H', 'e', 'l', 'l', 'o', 0, 0, 0, 0x02, 0x00};
    processPacket(buffer);
    return 0;
}

In the fixed code, we parse each component of the buffer independently, which avoids reliance on the struct's memory layout. This approach ensures that the code is portable and free from undefined behavior related to memory layout assumptions. By manually accessing each part of the buffer, we ensure that the code remains consistent across different compilers and architectures.