Heap Overflow Vulnerabilities and Concerned Threats

Introduction

Heap overflow vulnerabilities are memory corruption flaws that occur when an application writes beyond the boundaries of dynamically allocated memory. Heap memory stores runtime objects, buffers, pointers, and application states. An out-of-bound write can corrupt this data, causing crashes, data manipulation, denial of service, or, in some cases, arbitrary code execution.

Unlike stack-based overflows, heap-based buffer overflows depend heavily on memory layout, allocator behavior, application logic, and runtime protections. Understanding how heap memory corruption occurs is therefore important for developers, security engineers, and vulnerability management teams responsible for reducing exploitable risk.

What Is Heap Overflow?

A heap overflow is a type of memory corruption vulnerability that occurs when a program writes more data to a heap-allocated memory area than the space allocated for it. The excess data can overwrite adjacent memory, potentially causing application crashes, data corruption, or arbitrary code execution.

Understanding Heap Memory

Heap memory is an area of memory that applications use to store data while they are running. With dynamic memory allocation, an application can request memory when it needs it and release that memory when it is no longer needed.

Applications use heap memory when they need flexible storage, especially when the amount of memory required is not known in advance. It is commonly used for dynamically sized data, objects, and other information that may need to remain available while the program runs.

What Causes a Heap Overflow?

A heap overflow usually occurs when an application does not properly control how much data is written to a buffer. Common causes include insufficient bounds checking, unsafe memory operations, incorrect size calculations, and improper input validation.

For example, if an application allocates too little memory or accepts more data than a buffer can hold, the excess data may be written beyond the buffer's limits. The resulting out-of-bounds write can overwrite nearby memory and corrupt adjacent objects.

Heap Overflow vs. Buffer Overflow

A buffer overflow occurs when a program writes more data than a memory buffer can hold. A heap overflow is a type of buffer overflow that affects heap memory. Buffer overflows can affect different memory regions, while heap overflows specifically affect dynamically allocated memory. Their impact can include memory corruption, crashes, and other security consequences.

How Heap Overflow Works

A heap overflow attack can occur when attacker-controlled input causes an application to write beyond an allocated buffer. When the application writes this data without proper bounds checking, it can overwrite nearby heap data or change the application's state.  

Memory Allocation and Adjacent Heap Objects

These allocations can be placed near other objects in memory. When one buffer is overwritten, nearby objects may also be affected. This can lead to heap memory corruption and change how the application processes data.

How Out-of-Bounds Writes Corrupt Memory

When an application writes beyond the end of a heap-allocated buffer, the additional data can overwrite memory belonging to nearby objects. Depending on what is overwritten, this may corrupt application data, modify pointers, or alter the state of an object.

The security impact depends on the location and type of memory that is corrupted. A simple overwrite may cause an application crash, while corruption of security-sensitive data or control structures can create conditions for more serious exploitation.

Potential Exploitation Paths

The impact of heap overflow exploitation depends on what memory is overwritten and what security protections are in place. Possible outcomes include application crashes, data corruption, altered application behavior, or impacts to security boundaries.. In more serious cases, an attacker may achieve arbitrary code execution, but this depends on the specific vulnerability and available mitigations.

Why Heap Overflow Is Dangerous

Heap memory corruption can affect runtime objects and security-sensitive structures stored in nearby allocations.  

Denial of Service and Application Crashes

Corrupted pointers, invalid object state, or allocator inconsistencies can terminate an application. For network services and infrastructure tools, this can result in service disruption or repeated crashes.

Data Corruption and Information Exposure

A corrupted heap object can cause unexpected application behavior or incorrect data processing. Heap-based buffer over-reads are a related but different issue. They access memory beyond the intended buffer and may expose information that should not be returned to the caller.

Arbitrary Code Execution Risk

CWE-122 lists code execution as a potential consequence of heap-based buffer overflows. If an attacker gains sufficient control over security-relevant memory and bypasses available protections, the memory corruption may be leveraged to execute attacker-controlled code.

Why Exploitability Depends on the Environment

Exploitability varies according to memory layout, allocator implementation, compiler protections, ASLR, process privileges, and application architecture. Security teams should assess each heap overflow based on technical severity and real-world exposure rather than assuming every CVE carries the same risk.

Heap Overflow Vulnerabilities: Real-World Examples

Heap handles the dynamic storage of the data. One has to manually allocate and de-allocate the memory in heap storage using the malloc() and calloc() functions. When the memory management process is neglected, a heap overflow occurs which can affect the entire system code drastically.

• When de-allocating the memory space is ignored after use
• When large data variables are allocated

1.Heap overflow in vulnerability-1 in Tcpreplay

CWE: 122 -Heap Based Buffer Overflow

‍CVE number: CVE-2018-18407

‍Identified in: Appenta

‍Product Details: Tcpreplay is an open source software which helps to edit and replay the captured network traffic.

‍Vulnerability Specifics: The Tcpreplay research made by Loginsoft team has led to identify the heap overflow when a crafted pcap file is sent to Tcpreplay edit.

Epitome:

• Initially the csum_replace4() function of tcp_edit.c investigates for the checksum of level 4 headers.
• When such headers are sent , the code access the checksum of 16th offset in tcp header and a 66 relative to the buffer start.
• Ipv4_134_csum_replace() function is used to perform the checksum.
• Now, the heap overflow occurs when an invalid IP header is taken or when Ipv4_134_csum_replace() function ignores to check the buffer space before the editing of packets.

Check out the Detailed Report

‍Impact:

               Denial of Service

2.Heap based buffer over read vulnerability-2 in Tcpreplay

CWE: 126- Buffer Over-read

‍CVE number: CVE-2018-17974

‍Identified in: Appenta

Product Details: Tcpreplay is an open source software which helps to edit and replay the captured network traffic.

Vulnerability Specifics: The heap buffer over-read was encountered in tcpreplay-edit which encompasses both Tcpreplay and tcprewrite.

Read More

Epitome:

• In the version 4.3.0 beta 1 while the function dlt_n10mb_encode() residing in the file plugins/dle_en10mb/en10mb.c is executed with the in appropriate values of memmove().
• The length of the heap assigned for packet receiving is less than the source size and is resulting in the data over-ride.

Click here for detailed report

‍Impact:

• Denial of Service
• Un-authorized access
• Memory leaks

3.Heap based buffer over read vulnerability-3 in Tcpreplay

CWE: 126- Buffer Over-read

‍CVE number: CVE-2018-17580

‍Identified in: Appenta

Product Details: Tcpreplay is an open source software which helps to edit and replay the captured network traffic.

Vulnerability Specifics: The heap buffer over-read was encountered in when multiple data packets are sent into the same heap buffer with truncated packet lengths. The fast_edit_packet() function residing in the file send_packets.c which encompasses both Tcpreplay and tcprewrite.Read More

Epitome

• In the version 4.3.0 , send_packets() function is responsible for packet management and the fast_edit_package () function is called to check and validate the IP address uniqueness which directly increases the flows per second.
• Unlike the previous mention CVE-2018-17974 issue where the input packet length was greater than the max limit, here the received packet size is truncated and then further processed resulting in heap overflow.
• At last when such truncated packet is analyzed by wireshark, a message is being displayed to indicate about the truncation and also the third frame is corrupted as the total length of IP address field is not used.

Click here for detailed report

‍Impact:

‍Denial of Service

4.Heap based buffer over read vulnerability-4 in Tcpreplay

CWE:126- Buffer Over-read

‍CVE number: CVE-2018-17582

‍Identified in: Appenta

Product Details: Tcpreplay is an open source software which helps to edit and replay the captured network traffic.

Vulnerability Specifics: When the get_next_packet() function in the send_packets.c file utilizes the memcpy() to copy the sequences un-safely, a heap buffer over read is experienced.Read More

Epitome:

• When a pcap file is loaded into the RAM by preload_pcap_file() function, it is invoked by the swith-[K] which enable sthe caching of packets into internal memory.
• Then the get_next_packet() function is called to send the next packet out.
• Here, the packet utilizes memcpy()[3] where the received length field is invalid. This causes the invalid buffer reading beyond the limitations leading to heap over read.

Click here for detailed report

‍Impact:

• Denial of Service
• Un-authorized access
• Memory leaks

5.Heap based buffer over read vulnerability in HDF5

CWE:126- Buffer Over-read

‍CVE number: CVE-2018-17435

‍Identified in:: Hdfgroup

Product Details:HDF5 is totally into data managing side which effectively deals with all sorts of complex data and also provides tools and applications for analyzing the data in HDF5 format

Vulnerability Specifics:: A heap based buffer over-read is initialized when the function H5O_attr_decode() residing in H5Oattr.c file is executed through 1.10.3 library.Read More

Epitome:

• The h5LT_find_attribute()[1] is used to find the INTERLACE_MODE attribute to validate data sets and attributes whether they are attached with a particular name and an object loc_id.
• Then H5A_compact_build_table() is called to build a table which consists a list of attributes.
• Now, H5O_attr_decode() is called to decode the messages and return a pointer to memory struct. After few such attempts, the decode function attempts to get other data like data type and data space sizes by using HDmemcpy()[2].
• But due to incorrect and invalid inputs received in HDmemcpy() size filed, a heap buffer overflow occurs.

Click here for detailed report

‍Impact:

• Denial of Service
• Memory leaks

Heap Overflow vs. Stack Overflow

Heap overflow and stack overflow both represent memory-safety problems, but they affect different memory regions and can have different exploitation characteristics.

How Organizations Can Reduce the Risk of Heap Overflow

Effective heap overflow prevention requires controls across development, testing, and operations.

Secure Coding and Input Validation

Apply bounds checking before writes, validate externally supplied lengths, and avoid unsafe memory APIs where safer alternatives exist. These practices can prevent heap overflow conditions before deployment.

Code Review and Static Analysis

Use code review and static analysis to identify unchecked memory operations, unsafe functions, integer-size issues, and missing validation.

Dynamic Application Security Testing

Use fuzzing and instrumented builds with tools such as AddressSanitizer or Valgrind to detect memory corruption during runtime testing.

Dependency and Vulnerability Management

Track third-party libraries and prioritize vulnerabilities based on exploitability, asset exposure, business criticality, and available remediation.

Patch Management

Apply security fixes within a risk-based timeframe. EPSS and CISA KEV status can provide additional context when prioritizing vulnerabilities with known exploitation or a higher likelihood of exploitation.

Protection From Heap Overflows

Heap overflow protection works best as part of a defense-in-depth strategy.

Memory-Safety Protections

Compiler and runtime protections can detect or limit some memory corruption conditions. Allocator integrity checks can also make common corruption patterns harder to exploit.

Address Space Layout Randomization and Related Mitigations

ASLR randomizes memory locations, while PIE and related protections make useful addresses harder to predict. These mechanisms reduce exploit reliability but do not fix the underlying flaw.

Memory-Safe Programming Languages

Languages such as Rust use ownership and borrow checking to prevent many classes of memory-safety errors at compile time. Where practical, memory-safe components can reduce entire categories of heap vulnerabilities.

Continuous Vulnerability Monitoring

Continuous vulnerability monitoring helps identify newly disclosed heap vulnerabilities across operating systems, libraries, network tools, and application dependencies before they become overlooked risks.

Security Testing Across the SDLC

Combine static analysis during development, fuzzing and dynamic testing during QA, and continuous vulnerability monitoring after deployment. This creates layered coverage rather than relying on a single detection method.

Conclusion

A heap overflow vulnerability is a memory-safety flaw that can cause application crashes, denial of service, data corruption, information exposure, or, in some cases, arbitrary code execution. Heap overflow prevention requires more than secure coding alone. Organizations need memory-safe development practices, security testing, dependency visibility, and timely patching. Vulnerability research and layered runtime defenses can provide additional protection.

Loginsoft helps organizations identify, analyze, and prioritize vulnerabilities before they become exploitable threats. Its approach combines vulnerability research, threat intelligence, and continuous vulnerability monitoring.

Frequently Asked Questions  

Q1. What is a heap overflow vulnerability?

A heap overflow vulnerability is a type of memory corruption vulnerability that occurs when a program writes more data to a heap-allocated buffer than the amount of memory allocated for it.

Q2. What causes a heap overflow?

Common causes include inadequate bounds checking, unsafe memory operations, incorrect size calculations, and insufficient input validation. Examples of unsafe operations include unchecked memcpy() and strcpy() calls.

Q3. What is the difference between a heap overflow and a stack overflow?

A heap overflow affects dynamically allocated memory, while a stack overflow affects memory associated with function calls. Their exploitation techniques and applicable mitigations can therefore differ.

Q4. Can a heap overflow lead to remote code execution?

Yes. Some heap overflows can enable code execution if attackers gain sufficient control over security-relevant memory and bypass available mitigations. Exploitability depends on the vulnerability, application privileges, memory layout, allocator, and security controls.

Q5. How can heap overflow vulnerabilities be prevented?

Use secure memory-management practices, bounds checking, static and dynamic analysis, and fuzzing. Where appropriate, use memory-safe languages and maintain timely patching and continuous vulnerability management.

Q6. How are heap overflow vulnerabilities detected?

Detection can involve source-code review, static analysis, fuzzing, AddressSanitizer, Valgrind, and dynamic testing. Dependency scanning, vulnerability intelligence, and targeted security research can help identify affected software and prioritize remediation.

Q7. Why are heap-based buffer over-read vulnerabilities dangerous?

An out-of-bounds read accesses memory beyond the intended buffer. It may expose unintended data, cause application crashes, or provide information that supports further exploitation.

Q8. What security impact can a heap overflow have?

Potential impacts include denial of service, application crashes, data corruption, and information exposure. Under favorable conditions, a heap overflow may also enable memory manipulation or arbitrary code execution.