CVE-2018-25304 Overview
Free Download Manager 2.0 Built 417 contains a local buffer overflow vulnerability in the URL import functionality that allows attackers to trigger a structured exception handler (SEH) chain exploitation. Attackers can craft a malicious URL file that, when imported through the File > Import > Import lists of downloads menu, causes a buffer overflow in the Location header response that overwrites the SEH chain and executes arbitrary code.
Critical Impact
Successful exploitation allows an attacker to execute arbitrary code on the victim's system by convincing a user to import a malicious download list file.
Affected Products
- Free Download Manager 2.0 Built 417
Discovery Timeline
- 2026-04-29 - CVE CVE-2018-25304 published to NVD
- 2026-04-29 - Last updated in NVD database
Technical Details for CVE-2018-25304
Vulnerability Analysis
This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The flaw exists in how Free Download Manager handles the Location header when processing imported URL lists. The application fails to properly validate the size of data being copied into a fixed-size buffer, leading to memory corruption.
The local attack vector means an attacker must deliver a malicious file to the victim's system and convince them to import it through the application's import functionality. Once triggered, the overflow corrupts memory structures including the Structured Exception Handler (SEH) chain, a Windows mechanism for handling runtime errors. By carefully crafting the malicious input, attackers can hijack program execution flow when an exception is raised.
Root Cause
The root cause is improper bounds checking when processing the Location header during URL list imports. The application allocates a fixed-size buffer for storing header data but does not validate that incoming data fits within this boundary before copying. When an oversized Location header is processed, data overflows beyond the allocated buffer, corrupting adjacent memory including the SEH chain pointers stored on the stack.
Attack Vector
The attack requires local access and user interaction. An attacker must craft a malicious URL list file containing an oversized Location header designed to overflow the vulnerable buffer. The attack chain involves:
- Attacker creates a specially crafted URL import file with malicious Location header data
- Victim downloads or receives the malicious file through social engineering
- Victim opens Free Download Manager and navigates to File > Import > Import lists of downloads
- Upon importing the malicious file, the buffer overflow occurs
- The SEH chain is overwritten with attacker-controlled addresses
- When an exception triggers, execution flow redirects to attacker shellcode
The vulnerability mechanism involves overwriting SEH pointers with addresses pointing to executable shellcode embedded in the malicious payload. Technical details and proof-of-concept code are available through the Exploit-DB #44499 reference.
Detection Methods for CVE-2018-25304
Indicators of Compromise
- Presence of unusually large or malformed URL list files (.lst, .txt) containing oversized Location headers
- Free Download Manager crashes or unexpected termination during import operations
- Suspicious process behavior following URL list imports, including unexpected child processes or network connections
- Memory access violations or structured exception handling errors logged by Windows Event Viewer
Detection Strategies
- Monitor for Free Download Manager process crashes that could indicate exploitation attempts
- Implement file inspection rules to detect anomalously large headers in download list files before import
- Deploy endpoint detection rules that alert on SEH-based exploitation patterns
- Use application whitelisting to control which files can be imported into download managers
Monitoring Recommendations
- Enable Windows crash dump collection to capture exploitation attempts for forensic analysis
- Monitor process creation events where fdm.exe spawns unexpected child processes
- Deploy SentinelOne behavioral AI to detect post-exploitation activities following buffer overflow attacks
- Establish baseline behavior for Free Download Manager and alert on deviations
How to Mitigate CVE-2018-25304
Immediate Actions Required
- Upgrade to a newer version of Free Download Manager that addresses this buffer overflow vulnerability
- Avoid importing URL list files from untrusted or unknown sources
- Consider replacing Free Download Manager 2.0 Built 417 with a modern, actively maintained download manager
- Deploy endpoint protection solutions capable of detecting memory corruption exploits
Patch Information
No official vendor patch information is available for this specific build. The affected version (2.0 Built 417) is a legacy release. Users should upgrade to the latest version of Free Download Manager, which can be obtained from the official website. Review the VulnCheck Security Advisory for additional remediation guidance.
Workarounds
- Disable or restrict the import functionality if not required for business operations
- Implement application sandboxing to limit the impact of potential exploitation
- Configure endpoint security solutions to block execution of shellcode from stack memory regions
- Use Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR) to increase exploitation difficulty
- Restrict access to the vulnerable application to only trusted users who require the functionality
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
