CVE-2018-25299: Prime95 Buffer Overflow Vulnerability

CVE-2018-25299 Overview

CVE-2018-25299 is a local buffer overflow vulnerability affecting Prime95 version 29.4b8, a popular application used for stress testing CPUs and participating in the Great Internet Mersenne Prime Search (GIMPS) project. The vulnerability exists in the PrimeNet connection settings functionality, specifically within the optional proxy hostname field. Attackers can exploit this flaw to trigger a buffer overflow condition that overwrites structured exception handling (SEH) mechanisms, ultimately enabling arbitrary code execution on the target system.

Critical Impact

Successful exploitation allows attackers to execute arbitrary system commands with the privileges of the Prime95 process, potentially leading to complete system compromise through local access.

Affected Products

• Prime95 version 29.4b8
• Prime95 installations with PrimeNet connectivity features enabled
• Windows systems running vulnerable Prime95 versions

Discovery Timeline

• 2026-04-29 - CVE CVE-2018-25299 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2018-25299

Vulnerability Analysis

This vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input), a classic memory corruption issue that occurs when data is copied to a buffer without proper bounds checking. The flaw resides in how Prime95 processes user-supplied input in the proxy hostname configuration field within the PrimeNet connection settings dialog.

When a user enters an excessively long string in the proxy hostname field, the application fails to validate the input length before copying it to a fixed-size buffer. This oversight allows the attacker-controlled data to overflow beyond the allocated buffer boundaries, corrupting adjacent memory regions including the SEH chain.

The exploitation leverages Windows Structured Exception Handling mechanisms. By carefully crafting the overflow payload, an attacker can overwrite the SEH handler pointers with addresses pointing to malicious shellcode. When an exception is triggered (which can be forced as part of the overflow), the corrupted SEH handler executes the attacker's payload instead of legitimate exception handling code.

Root Cause

The root cause of CVE-2018-25299 is improper input validation in the proxy hostname processing routine. The application uses unsafe string copy operations that do not verify whether the input data exceeds the destination buffer's capacity. This is a fundamental secure coding violation where user-controlled input is directly copied to a stack-based buffer without length restrictions, enabling stack buffer overflow attacks that can hijack program execution flow through SEH manipulation.

Attack Vector

The attack vector for this vulnerability requires local access to the system running Prime95. An attacker must be able to interact with the Prime95 application interface or manipulate its configuration files. The exploitation process involves:

1. Accessing the Prime95 application's PrimeNet connection settings
2. Entering a specially crafted malicious string in the proxy hostname field
3. The oversized input overflows the buffer and corrupts the SEH chain on the stack
4. Triggering an exception causes the corrupted SEH handler to execute
5. The attacker's shellcode payload runs with the privileges of the Prime95 process

The vulnerability does not require authentication and has no user interaction requirements beyond the initial application access. The attack complexity is low, making it relatively straightforward to exploit for attackers with local system access. For detailed technical information about the exploitation technique, refer to the Exploit-DB entry #44649.

Detection Methods for CVE-2018-25299

Indicators of Compromise

• Unusual Prime95 process behavior or unexpected child processes spawning
• Crash dumps from Prime95 showing SEH chain corruption or stack overflow conditions
• Modified Prime95 configuration files (prime.txt or local.txt) containing abnormally long proxy hostname values
• Evidence of shellcode execution patterns in memory analysis following Prime95 crashes

Detection Strategies

• Monitor for Prime95 process crashes accompanied by access violation exceptions
• Implement application whitelisting to detect unauthorized code execution from Prime95 context
• Use endpoint detection and response (EDR) solutions to monitor for SEH overwrite patterns
• Deploy memory protection technologies that can detect stack buffer overflow attempts

Monitoring Recommendations

• Enable Windows Event Log monitoring for application crashes related to Prime95
• Configure security tools to alert on suspicious process creation from Prime95
• Implement file integrity monitoring on Prime95 configuration files
• Review endpoint telemetry for memory corruption exploitation indicators

How to Mitigate CVE-2018-25299

Immediate Actions Required

• Upgrade Prime95 to a patched version that addresses the buffer overflow vulnerability
• Restrict local access to systems running Prime95 to authorized users only
• Consider disabling PrimeNet connectivity features if not required for operations
• Apply defense-in-depth measures including DEP (Data Execution Prevention) and ASLR (Address Space Layout Randomization)

Patch Information

Users should download the latest version of Prime95 from the official Mersenne Download Page. The Mersenne Organization maintains the official Prime95 releases. Verify that your version is newer than 29.4b8 to ensure protection against this vulnerability. Additional technical details are available in the VulnCheck Advisory.

Workarounds

• Avoid using the PrimeNet proxy configuration feature until the application is updated
• Run Prime95 in an isolated environment or sandbox to contain potential exploitation
• Implement network segmentation to limit the impact of potential compromise
• Use application control policies to restrict Prime95 from spawning child processes