CVE-2026-42469: OVMS3 Buffer Overflow Vulnerability

CVE-2026-42469 Overview

CVE-2026-42469 is a stack-based buffer overflow [CWE-121] in the Open Vehicle Monitoring System 3 (OVMS3) version 3.3.005. The flaw resides in canformat_canswitch.cpp, where the parser fails to validate the Data Length Code (DLC) field of a CANswitch frame. Remote attackers can send crafted CANswitch frames to trigger a denial of service or potentially execute arbitrary code on the device. OVMS3 is an open-source telematics platform used to monitor and control electric vehicles, making this flaw relevant to connected vehicle deployments.

Critical Impact

Unauthenticated remote attackers can crash OVMS3 devices or execute arbitrary code by sending malformed CANswitch frames over the network.

Affected Products

• Open Vehicle Monitoring System 3 (OVMS3) version 3.3.005
• The vulnerable component is the canformat_canswitch.cpp CANswitch frame parser
• Deployments using the OVMS3 firmware to bridge CAN bus traffic over network interfaces

Discovery Timeline

• 2026-05-01 - CVE-2026-42469 published to the National Vulnerability Database
• 2026-05-07 - Last updated in the NVD database

Technical Details for CVE-2026-42469

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow classified under [CWE-121]. It is triggered when the OVMS3 CANswitch parser processes an attacker-controlled DLC value without bounds checking. A Controller Area Network (CAN) frame DLC field specifies the size of the data payload. When the parser uses an unvalidated DLC to copy frame data into a fixed-size stack buffer, the copy operation can write past the intended buffer boundary.

The writeup referenced in the GitHub Issue Discussion and the GitHub Gist PoC Reference describe the parsing path that processes incoming CANswitch frames. Because the input is reachable over the network without authentication, the attack complexity is low. The Exploit Prediction Scoring System (EPSS) probability for this CVE is 0.19% with a percentile of 40.58 as of 2026-05-07.

Root Cause

The root cause is the absence of an upper-bound check on the DLC value parsed from a CANswitch frame. The parser in canformat_canswitch.cpp trusts the attacker-supplied length and uses it to drive a memory copy into a stack-allocated buffer. Standard CAN frames cap payloads at 8 bytes and CAN FD at 64 bytes, but no enforcement is performed before the copy.

Attack Vector

An attacker delivers a crafted CANswitch frame to a network-reachable OVMS3 instance. The frame carries a DLC value larger than the destination buffer, overflowing adjacent stack memory including saved return addresses. Successful exploitation can corrupt control flow on the embedded ESP32-class target and cause denial of service or arbitrary code execution. No authentication or user interaction is required.

Verified exploitation code is not reproduced here. See the GitHub Gist PoC Reference for technical details.

Detection Methods for CVE-2026-42469

Indicators of Compromise

• Unexpected restarts, watchdog resets, or crash logs from OVMS3 devices that coincide with inbound CANswitch traffic
• CANswitch frames where the DLC field exceeds protocol-defined maximums (8 bytes for classic CAN, 64 bytes for CAN FD)
• Inbound network connections to OVMS3 listeners from unrecognized sources or geographies
• Memory corruption signatures in serial console output, including stack canary failures and invalid program counter values

Detection Strategies

• Inspect network traffic destined for OVMS3 devices and flag CANswitch frames with malformed or oversized DLC values
• Correlate device crash telemetry with concurrent network ingress events at the perimeter
• Monitor firmware logs for repeated canformat_canswitch parser errors that may precede successful exploitation

Monitoring Recommendations

• Forward OVMS3 device logs and crash dumps to a centralized logging or SIEM platform for long-term retention and correlation
• Baseline normal CANswitch frame rates and alert on volume spikes or anomalous source addresses
• Track firmware versions across the fleet so any device still running 3.3.005 is flagged for prioritized remediation

How to Mitigate CVE-2026-42469

Immediate Actions Required

• Inventory all OVMS3 devices and identify any running version 3.3.005 of the firmware
• Restrict network exposure of OVMS3 management and CANswitch interfaces to trusted management networks only
• Apply firewall or access control list rules that drop CANswitch frames from untrusted sources
• Monitor the GitHub Issue Discussion for an upstream fix and apply it once available

Patch Information

No vendor patch advisory was listed at the time of NVD publication. Operators should track the upstream Open-Vehicle-Monitoring-System-3 repository for a fix to the canformat_canswitch.cpp DLC validation logic and update affected devices once a patched release is published.

Workarounds

• Place OVMS3 devices behind a VPN or segmented management network to remove direct internet exposure
• Disable the CANswitch ingress path on devices that do not require it
• Apply ingress filtering that drops CAN frames where the DLC exceeds protocol maximums before they reach the parser
• Increase logging verbosity on OVMS3 devices to capture early signs of malformed-frame parsing failures

# Example: restrict OVMS3 network exposure to a trusted management subnet
# Replace eth0 and 10.0.0.0/24 with the interface and trusted CIDR for your environment
iptables -A INPUT -i eth0 -s 10.0.0.0/24 -p tcp --dport 6867 -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --dport 6867 -j DROP
iptables -A INPUT -i eth0 -s 10.0.0.0/24 -p udp --dport 6867 -j ACCEPT
iptables -A INPUT -i eth0 -p udp --dport 6867 -j DROP