CVE-2025-66215: OpenSC Buffer Overflow Vulnerability

CVE-2025-66215 Overview

CVE-2025-66215 is a stack-based buffer overflow vulnerability affecting OpenSC, an open source smart card tools and middleware package. Prior to version 0.27.0, an attacker with physical access to the computer when a user or administrator uses a token can trigger a stack-buffer-overflow WRITE condition in the card-oberthur component. The attack requires a crafted USB device or smart card that presents the system with specially crafted responses to APDU (Application Protocol Data Unit) commands.

Critical Impact

Physical access exploitation enables potential arbitrary code execution through stack buffer overflow, affecting confidentiality, integrity, and availability of systems using OpenSC for smart card authentication.

Affected Products

• OpenSC versions prior to 0.27.0
• Systems using card-oberthur driver for Oberthur smart cards
• Any application relying on OpenSC middleware for smart card operations

Discovery Timeline

• 2026-03-30 - CVE-2025-66215 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2025-66215

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when data is written beyond the boundaries of a stack-allocated buffer. The vulnerable component is the card-oberthur driver within OpenSC, which handles communication with Oberthur smart cards.

The attack requires physical proximity—an attacker must either connect a malicious USB device or insert a crafted smart card into a reader attached to the target system. When the victim system processes APDU responses from the malicious device, the card-oberthur driver fails to properly validate the length of incoming data before copying it to a stack buffer, resulting in a buffer overflow condition.

Successful exploitation could allow an attacker to overwrite adjacent stack memory, potentially corrupting return addresses or other critical data structures. This can lead to arbitrary code execution in the context of the application using OpenSC, compromising system confidentiality, integrity, and availability.

Root Cause

The root cause is insufficient bounds checking in the card-oberthur driver when processing APDU responses from smart cards. The driver allocates a fixed-size buffer on the stack but does not properly validate that incoming response data fits within this buffer before performing the write operation. When a malicious device returns oversized or malformed APDU responses, the driver blindly writes past the buffer boundary.

Attack Vector

The attack requires physical access to insert a malicious smart card or connect a crafted USB device to the target system. The attacker must time the attack to coincide with when a legitimate user or administrator actively uses a token, as the vulnerable code path is only triggered during smart card operations. The malicious device must be crafted to return specially formatted APDU responses that exploit the buffer overflow condition in the card-oberthur driver.

The physical access requirement limits the attack surface, but in shared computing environments, kiosk systems, or scenarios where smart card readers are accessible, this vulnerability poses a significant risk for privilege escalation or code execution.

Detection Methods for CVE-2025-66215

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using OpenSC for smart card authentication
• Unusual USB device connection events, particularly unknown smart card reader devices
• Memory corruption errors logged by system monitoring tools during smart card operations
• Anomalous behavior following smart card insertion events

Detection Strategies

• Monitor system logs for crashes or errors related to opensc-pkcs11, opensc-tool, or other OpenSC components
• Implement USB device allowlisting to prevent unauthorized smart card readers from connecting
• Deploy endpoint detection solutions that can identify memory corruption exploitation attempts
• Use crash dump analysis to identify stack overflow patterns in OpenSC-related processes

Monitoring Recommendations

• Enable detailed logging for smart card operations and APDU communication when feasible
• Monitor for unexpected process terminations or memory access violations in OpenSC-related services
• Track USB device insertion events and correlate with any subsequent system anomalies
• Review authentication logs for failed or anomalous smart card authentication attempts

How to Mitigate CVE-2025-66215

Immediate Actions Required

• Upgrade OpenSC to version 0.27.0 or later immediately on all affected systems
• Restrict physical access to systems using smart card authentication where possible
• Implement USB device allowlisting to prevent unauthorized devices from connecting
• Consider temporarily disabling smart card functionality on critical systems until patching is complete

Patch Information

OpenSC has addressed this vulnerability in version 0.27.0. The fix is available through the GitHub Commit and was introduced via Pull Request 3436. Additional details are available in the GitHub Security Advisory GHSA-q5fc-cw56-hwp2 and the CVE-2025-66215 Wiki page.

Workarounds

• Implement strict physical security controls to prevent unauthorized USB device connections
• Use USB port blocking solutions or hardware locks on systems where smart card functionality is not required
• Deploy endpoint protection that monitors for and blocks suspicious USB device activity
• If Oberthur smart cards are not in use, consider disabling or removing the card-oberthur driver

# Verify OpenSC version to confirm patch status
opensc-tool --version

# If running a vulnerable version, upgrade to 0.27.0 or later
# On Debian/Ubuntu systems:
sudo apt update && sudo apt install opensc

# On RHEL/CentOS systems:
sudo dnf update opensc

# On systems using source installation, rebuild from patched source:
git clone https://github.com/OpenSC/OpenSC.git
cd OpenSC
git checkout tags/0.27.0
./bootstrap && ./configure && make && sudo make install