CVE-2025-67433 Overview
A heap buffer overflow vulnerability exists in the processRequest function of Open TFTP Server MultiThreaded v1.7. This vulnerability allows remote attackers to cause a Denial of Service (DoS) condition by sending specially crafted DATA packets to the server. The vulnerability stems from improper bounds checking when processing incoming TFTP protocol data, leading to memory corruption in the heap region.
Critical Impact
Remote attackers can crash the TFTP server by sending malicious DATA packets, disrupting file transfer services and potentially affecting critical infrastructure that relies on TFTP for firmware updates, configuration management, or network booting.
Affected Products
- Open TFTP Server MultiThreaded v1.7
- Systems running vulnerable TFTP server configurations
- Network infrastructure relying on TFTP services for PXE boot or firmware distribution
Discovery Timeline
- 2026-02-12 - CVE-2025-67433 published to NVD
- 2026-02-12 - Last updated in NVD database
Technical Details for CVE-2025-67433
Vulnerability Analysis
This heap buffer overflow vulnerability occurs within the processRequest function, which is responsible for handling incoming TFTP protocol requests. When the server receives a DATA packet, the function fails to properly validate the size of the incoming data before copying it to a heap-allocated buffer.
TFTP (Trivial File Transfer Protocol) operates over UDP on port 69 and uses a simple packet structure. DATA packets contain a 2-byte opcode, a 2-byte block number, and up to 512 bytes of data. The vulnerability is triggered when an attacker sends a malformed DATA packet with content that exceeds the expected buffer boundaries, causing the server to write beyond the allocated heap memory region.
The exploitation results in heap memory corruption, which immediately causes the TFTP server process to crash. While the current analysis indicates this vulnerability is limited to Denial of Service, heap overflows can potentially be leveraged for more severe attacks depending on the memory layout and exploitation techniques employed.
Root Cause
The root cause of this vulnerability is insufficient input validation in the processRequest function. The function allocates a fixed-size heap buffer to store incoming DATA packet contents but does not properly verify that the received data length fits within the allocated buffer space before performing the memory copy operation. This classic heap buffer overflow pattern occurs when the application trusts the length of attacker-controlled input without proper bounds checking.
Attack Vector
The attack can be executed remotely over the network by any attacker who can send UDP packets to the TFTP server on port 69. The attacker crafts a malicious DATA packet with an oversized payload or manipulated length fields. When the vulnerable server processes this packet, the heap buffer overflow occurs, corrupting adjacent heap metadata or memory regions and causing the server to crash.
The attack requires no authentication as TFTP is an unauthenticated protocol by design. An attacker simply needs network connectivity to the target TFTP server to exploit this vulnerability. A proof-of-concept demonstrating this vulnerability has been published to GitHub Gist.
Detection Methods for CVE-2025-67433
Indicators of Compromise
- Unexpected TFTP server crashes or service restarts
- Anomalous UDP traffic to port 69 with oversized or malformed DATA packets
- Core dumps or crash logs indicating heap corruption in the TFTP server process
- Network traffic containing TFTP DATA packets with unusual payload sizes
Detection Strategies
- Monitor TFTP server logs and system logs for unexpected process terminations
- Implement network intrusion detection rules to identify malformed TFTP packets
- Deploy endpoint detection and response (EDR) solutions to detect heap corruption attempts
- Configure alerts for TFTP server availability and automatic restart events
Monitoring Recommendations
- Enable detailed logging on TFTP servers to capture packet-level information
- Monitor for repeated TFTP server crashes which may indicate exploitation attempts
- Implement network segmentation to limit exposure of TFTP services
- Use SentinelOne Singularity platform to detect and respond to memory corruption attacks in real-time
How to Mitigate CVE-2025-67433
Immediate Actions Required
- Restrict network access to the TFTP server using firewall rules to allow only trusted IP addresses
- Consider disabling the TFTP service if not actively required
- Implement network segmentation to isolate TFTP servers from untrusted networks
- Monitor for vendor patches or updates for Open TFTP Server MultiThreaded
Patch Information
At the time of publication, no official patch has been released for this vulnerability. Users should monitor the SourceForge project page for updates and security releases. Consider migrating to an alternative TFTP server implementation with active security maintenance if patches are not forthcoming.
Workarounds
- Deploy firewall rules to restrict TFTP access to specific trusted IP addresses only
- Place TFTP servers behind a reverse proxy or application-layer gateway that can filter malicious packets
- Consider using alternative file transfer protocols (SFTP, SCP) where TFTP functionality is not strictly required
- Implement rate limiting on UDP port 69 to reduce the impact of repeated exploitation attempts
- Run the TFTP server in a containerized or sandboxed environment to limit the impact of crashes
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
