CVE-2025-24956: Siemens OpenV2G Buffer Overflow Flaw

CVE-2025-24956 Overview

A buffer overflow vulnerability has been identified in Siemens OpenV2G, an open-source implementation of the ISO 15118 Vehicle-to-Grid (V2G) communication protocol. The vulnerability exists in the EXI (Efficient XML Interchange) parsing feature, specifically in the handling of X509 serial numbers. Due to a missing length check during parsing operations, an attacker can trigger a buffer overflow condition that leads to memory corruption.

Critical Impact

Successful exploitation of this buffer overflow vulnerability could allow an attacker to cause memory corruption, potentially leading to denial of service conditions in electric vehicle charging infrastructure systems.

Affected Products

• Siemens OpenV2G (All versions prior to V0.9.6)

Discovery Timeline

• February 11, 2025 - CVE-2025-24956 published to NVD
• September 24, 2025 - Last updated in NVD database

Technical Details for CVE-2025-24956

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), a classic buffer overflow condition. The flaw resides in OpenV2G's EXI parsing functionality, which processes Efficient XML Interchange formatted data used in V2G communication protocols for electric vehicle charging.

When parsing X509 serial numbers within the EXI data stream, the parsing routine fails to validate the length of incoming serial number data before copying it into a fixed-size buffer. This oversight creates a situation where an attacker can supply an X509 serial number exceeding the expected buffer size, causing data to overflow into adjacent memory regions.

The local attack vector requires an attacker to have access to the system running OpenV2G or to supply maliciously crafted EXI data through legitimate communication channels. While no user interaction is required, the attacker does not need prior privileges to exploit this vulnerability.

Root Cause

The root cause is a missing boundary check in the EXI parsing code path that handles X509 certificate serial numbers. When processing incoming EXI-encoded data containing X509 certificates, the parser allocates a fixed-size buffer for the serial number field but fails to verify that the incoming data length does not exceed this allocation. This violates secure coding principles that mandate input validation before memory operations.

Attack Vector

The attack vector is local, meaning an attacker would need to deliver maliciously crafted EXI data to a system running the vulnerable OpenV2G library. In the context of V2G infrastructure, this could occur through:

1. A compromised or malicious electric vehicle communicating with a charging station
2. A rogue charging station communicating with a vehicle's onboard system
3. Man-in-the-middle attacks on V2G communication channels where an attacker can inject malformed EXI data

The attacker constructs an EXI payload containing an X509 certificate with an oversized serial number field. When the vulnerable OpenV2G instance parses this data, the buffer overflow occurs, corrupting adjacent memory structures and potentially causing system instability or crashes.

Detection Methods for CVE-2025-24956

Indicators of Compromise

• Unexpected crashes or service interruptions in OpenV2G-based applications
• Memory corruption errors or segmentation faults in system logs related to V2G services
• Abnormal EXI parsing activity with unusually large X509 certificate data
• Core dump files indicating buffer overflow conditions in the OpenV2G parsing modules

Detection Strategies

• Monitor V2G communication endpoints for anomalous EXI payloads containing oversized X509 serial number fields
• Implement application-level logging to capture and analyze EXI parsing operations
• Deploy memory protection mechanisms (ASLR, stack canaries) to detect and mitigate overflow attempts
• Use intrusion detection rules to flag X509 certificate data exceeding normal size thresholds

Monitoring Recommendations

• Enable verbose logging on OpenV2G instances to capture parsing errors and exceptions
• Monitor system stability metrics for V2G infrastructure components running vulnerable versions
• Implement network traffic analysis for V2G communication protocols to identify malformed messages
• Review crash reports and memory dump analysis for signs of exploitation attempts

How to Mitigate CVE-2025-24956

Immediate Actions Required

• Upgrade OpenV2G to version V0.9.6 or later immediately
• Audit all deployments to identify systems running vulnerable OpenV2G versions
• Implement network segmentation to limit exposure of V2G infrastructure
• Enable memory protection features (DEP/NX, ASLR) on systems running OpenV2G

Patch Information

Siemens has released version V0.9.6 of OpenV2G which addresses this vulnerability by implementing proper length validation for X509 serial numbers during EXI parsing. Organizations should review the Siemens Security Advisory SSA-647005 for detailed patch information and update guidance.

Workarounds

• Restrict network access to V2G communication interfaces to trusted systems only
• Implement input validation at network boundaries to filter malformed EXI data before it reaches OpenV2G
• Deploy application firewalls or proxies capable of inspecting V2G protocol traffic
• Consider temporarily isolating vulnerable systems until patching can be completed

# Configuration example - Network isolation for V2G infrastructure
# Restrict access to V2G service ports (example using iptables)
iptables -A INPUT -p tcp --dport 15118 -s trusted_network/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 15118 -j DROP