CVE-2026-42468: OVMS3 Buffer Overflow Vulnerability

CVE-2026-42468 Overview

CVE-2026-42468 is a stack-based buffer overflow [CWE-121] in Open Vehicle Monitoring System 3 (OVMS3) version 3.3.005. The flaw resides in canformat_pcap.cpp, where the parser fails to validate the phdr.len field before processing PCAP input. Remote attackers who deliver a crafted PCAP file can trigger a denial of service or potentially execute arbitrary code on the affected device. OVMS3 is an open-source telematics platform deployed on electric and hybrid vehicles, making the impact relevant to both vehicle owners and fleet operators.

Critical Impact

A crafted PCAP file processed by OVMS3 can crash the device or lead to arbitrary code execution on the vehicle telematics module.

Affected Products

• Open Vehicle Monitoring System 3 (OVMS3) version 3.3.005
• Deployments using canformat_pcap.cpp for CAN bus PCAP parsing
• Vehicle telematics modules running the affected OVMS3 firmware

Discovery Timeline

• 2026-05-01 - CVE-2026-42468 published to NVD
• 2026-05-07 - Last updated in NVD database

Technical Details for CVE-2026-42468

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow in the OVMS3 PCAP parser implemented in canformat_pcap.cpp. PCAP files contain per-packet headers that include a length field (phdr.len) describing the size of the packet payload. The parser reads this attacker-controlled length and uses it to copy packet data into a fixed-size stack buffer without bounds checking. When phdr.len exceeds the destination buffer size, adjacent stack memory is overwritten, including saved return addresses and frame pointers.

The attack requires user interaction, meaning an operator must import or load a malicious PCAP file into OVMS3. Successful exploitation can corrupt control-flow data and lead to arbitrary code execution within the OVMS3 process context. Because OVMS3 interfaces with vehicle CAN bus traffic, code execution on the module can extend influence over downstream vehicle communications.

Root Cause

The root cause is missing input validation on the phdr.len field parsed from untrusted PCAP input. The parser treats the length as trusted and uses it directly in a memory copy operation. Proper validation would compare phdr.len against both the maximum supported packet size and the destination buffer capacity before any copy occurs.

Attack Vector

Exploitation is network-reachable but requires user interaction to load the malicious PCAP. An attacker crafts a PCAP file with a packet header whose phdr.len value exceeds the parser's destination buffer. When the file is imported into OVMS3 for replay or analysis, the oversized length triggers the overflow. Refer to the GitHub Issue Discussion and the GitHub Gist Code Snippet for technical reproduction details.

Detection Methods for CVE-2026-42468

Indicators of Compromise

• Unexpected crashes or restarts of the OVMS3 process when loading or replaying PCAP files
• Presence of unsolicited or externally sourced .pcap files in OVMS3 storage directories
• Anomalous CAN bus traffic patterns originating from the OVMS3 module after PCAP import

Detection Strategies

• Inspect PCAP files prior to import and reject any where the per-packet phdr.len exceeds the maximum expected CAN frame size
• Monitor OVMS3 logs for parser errors, segmentation faults, or abnormal terminations associated with canformat_pcap
• Correlate file transfer events to OVMS3 with subsequent process crashes to identify exploitation attempts

Monitoring Recommendations

• Enable verbose logging on OVMS3 components handling PCAP parsing and forward logs to a central collector
• Track integrity of OVMS3 binaries and configuration to detect post-exploitation modifications
• Alert on PCAP files arriving from untrusted sources or via unexpected channels such as USB or HTTP uploads

How to Mitigate CVE-2026-42468

Immediate Actions Required

• Restrict PCAP file imports to trusted operators and validated sources only
• Disable or remove access to the PCAP replay and analysis features in OVMS3 until a patched build is available
• Isolate OVMS3 modules from untrusted networks and limit remote management interfaces

Patch Information

No official patched release is referenced in the CVE record at the time of publication. Track the upstream GitHub Issue Discussion for fix availability and apply updates from the Open-Vehicle-Monitoring-System-3 project as soon as a corrected build is published.

Workarounds

• Validate every PCAP file out-of-band by confirming phdr.len does not exceed the maximum expected frame size before importing into OVMS3
• Run OVMS3 with the least privileges required and apply operating system level memory protections such as stack canaries and ASLR where supported
• Maintain offline backups of OVMS3 configuration to enable rapid recovery after a crash or compromise