CVE-2026-103531 in OpenSC
Summary
by MITRE • 10/01/2026
A flaw has been found in OpenSC up to 0.27.1. The impacted element is the function setcos_construct_fci_44 of the file src/libopensc/card-setcos.c. Executing a manipulation of the argument type_attr can lead to stack-based buffer overflow. The attack can be launched remotely. This patch is called ad730304052937c32b4eb489a06835ac6123632c. It is best practice to apply a patch to resolve this issue.
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability identified in OpenSC versions up to 0.27.1 represents a critical security flaw located within the cryptographic smart card management library, specifically affecting the function setcos_construct_fci_44 found in the source file src/libopensc/card-setcos.c. This component is responsible for handling File Control Information (FCI) structures used during communication with COS-based smart cards. The core technical issue stems from a stack-based buffer overflow triggered by improper validation of input data, particularly when manipulating the argument type_attr. In C programming environments, functions that handle string or binary data without rigorous bounds checking are susceptible to overwriting adjacent memory locations on the call stack. When an attacker provides a crafted value for type_attr that exceeds the expected buffer size, it causes the program to write beyond the allocated stack space, potentially corrupting return addresses and other critical control data structures stored in that region of memory.
From a technical perspective, this flaw aligns with CWE-121, which describes a stack-based buffer overflow condition where user-controlled input is copied into a fixed-size buffer without adequate length verification. The vulnerability allows for arbitrary code execution if the attacker can precisely craft the payload to overwrite the return address or function pointers on the stack. Given that OpenSC serves as an intermediary between applications and smart card hardware, this flaw exposes the underlying system to remote exploitation scenarios where malicious actors can send specially crafted commands through supported interfaces such as PC/SC. The ability to launch attacks remotely significantly increases the risk profile, as it does not require physical access to the target machine or local authentication privileges in many deployment configurations involving networked smart card readers or virtualized environments.
The operational impact of this vulnerability is severe, potentially leading to complete system compromise. An attacker exploiting this stack-based buffer overflow could execute arbitrary code with the privileges of the process running OpenSC. In typical deployments where OpenSC runs under a user account managing digital certificates and private keys, successful exploitation might allow an adversary to extract sensitive cryptographic material, impersonate legitimate users in authentication processes, or pivot further into internal networks by leveraging compromised credentials stored on smart cards. Furthermore, because this function is part of the core library handling card communication protocols, it affects multiple applications that rely on OpenSC for secure key management and digital signature operations, thereby amplifying the blast radius across enterprise security infrastructures dependent on PKI and hardware-backed identity solutions.
To mitigate this risk, immediate action is required to apply the patch identified by commit hash ad730304052937c32b4eb489a06835ac6123632c. This update addresses the input validation logic within setcos_construct_fci_44, ensuring that buffer sizes are strictly enforced before data copying operations occur. Organizations should prioritize updating their OpenSC installations to version 0.27.2 or later across all systems utilizing smart card authentication and management services. Additionally, implementing defense-in-depth strategies such as enabling stack protection mechanisms like Stack Canaries (CWE-124) in compiler flags during the build process can provide an additional layer of runtime detection for buffer overflow attempts. Monitoring system logs for unusual activity related to PC/SC service interactions and restricting network access to smart card readers where possible further reduces the attack surface associated with this remote exploit vector aligned with ATT&CK techniques involving exploitation of client-side software components.