CVE-2026-37541 Overview
CVE-2026-37541 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_gvret.cpp, where the length field embedded in Generic Vehicle Reverse Engineering Tool (GVRET) binary frames is not validated before data is copied into a fixed-size buffer. Remote attackers can send crafted GVRET frames to trigger memory corruption, leading to denial of service or arbitrary code execution on the vehicle telematics device. The CVE was published on 2026-05-01 and last modified on 2026-05-07.
Critical Impact
Unauthenticated network attackers can corrupt memory on OVMS3 devices, enabling remote code execution against connected vehicles and their telematics infrastructure.
Affected Products
- Open Vehicle Monitoring System 3 (OVMS3) version 3.3.005
- OVMS3 firmware builds containing canformat_gvret.cpp with the unchecked length field
- Deployments using GVRET binary frame ingestion on OVMS3
Discovery Timeline
- 2026-05-01 - CVE-2026-37541 published to the National Vulnerability Database
- 2026-05-07 - Last updated in NVD database
Technical Details for CVE-2026-37541
Vulnerability Analysis
The vulnerability is a classic stack-based buffer overflow in the GVRET protocol parser of OVMS3. The GVRET format encodes a length value inside each binary frame, which the parser uses to determine how many bytes to copy from the incoming frame into a local buffer. The parser in canformat_gvret.cpp trusts this attacker-controlled length without comparing it against the destination buffer size.
When an attacker supplies a length larger than the buffer, the copy operation overruns adjacent stack memory. This can overwrite saved return addresses, function pointers, or other stack-resident structures used by the OVMS3 firmware. On the ESP32-class hardware that OVMS3 targets, this corruption produces immediate process failure or, with frame contents shaped to redirect control flow, arbitrary code execution within the firmware context.
Root Cause
The root cause is missing input validation on the GVRET length field [CWE-121]. The parser dereferences and uses the length directly as a copy size without bounds checking against the destination buffer. There is no maximum-length constant enforced and no defensive truncation, so any malformed frame that declares an oversized payload will trigger the overflow.
Attack Vector
Exploitation requires only network reachability to the GVRET interface exposed by OVMS3. No authentication or user interaction is needed, and the scope is changed because corruption of the firmware can affect connected vehicle subsystems. An attacker crafts a GVRET binary frame containing an inflated length field followed by payload bytes shaped to hijack control flow, then transmits it to the device.
The vulnerability mechanism is described in prose only as no verified exploitation code is provided. Refer to the GitHub Gist PoC and the GitHub Issue #1393 Discussion for technical details.
Detection Methods for CVE-2026-37541
Indicators of Compromise
- GVRET frames with length fields exceeding the documented maximum payload size for the protocol
- Unexpected reboots, watchdog resets, or crash logs on OVMS3 devices following inbound GVRET traffic
- Outbound connections from OVMS3 devices to unfamiliar hosts after malformed frame ingestion
- New or modified processes within the OVMS3 firmware runtime not associated with normal vehicle telemetry
Detection Strategies
- Inspect GVRET traffic at network egress and ingress points and alert on frames whose declared length exceeds protocol-defined limits
- Monitor OVMS3 device logs for parser errors, stack canary failures, or crash dumps originating in canformat_gvret.cpp
- Apply network intrusion detection signatures that identify oversized GVRET binary frames sent to OVMS3 listeners
Monitoring Recommendations
- Capture and retain packet metadata for all traffic to and from OVMS3 management interfaces
- Track firmware version and build identifiers across the fleet to identify devices still running 3.3.005
- Correlate vehicle telematics anomalies with network events targeting OVMS3 endpoints
How to Mitigate CVE-2026-37541
Immediate Actions Required
- Restrict network access to OVMS3 GVRET interfaces using firewall rules or VPN-only reachability
- Disable GVRET ingestion on OVMS3 devices that do not require it for operational use
- Inventory all OVMS3 deployments and confirm which units run firmware 3.3.005
Patch Information
No fixed firmware version is listed in the NVD entry at publication. Track the Open Vehicles Project Repository and GitHub Issue #1393 Discussion for upstream commits that add length validation to canformat_gvret.cpp. Apply the corrected firmware build to all affected devices once published.
Workarounds
- Place OVMS3 devices on isolated network segments with strict allowlists for trusted management hosts
- Block inbound GVRET binary frames at the network perimeter when the protocol is not in active use
- Rebuild OVMS3 firmware from source with a local patch that validates the GVRET length field against the destination buffer size before copying
# Example: restrict OVMS3 device reachability with iptables
iptables -A INPUT -p tcp --dport 1000 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 1000 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
