CVE-2026-21129 in Checkout
Summary
by MITRE • 10/12/2026
Improper input validation in GuestCreditCardRegisterActivity of Samsung Checkout prior to version 5.1.03.1 allows local attackers to launch an arbitrary activity with Samsung Checkout privileges.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified within the Samsung Checkout application, specifically affecting versions prior to 5.1.03.1, stems from a critical failure in input validation mechanisms located within the GuestCreditCardRegisterActivity component. This Android Activity is designed to handle user inputs for registering credit card information during guest checkout processes. However, the underlying implementation fails to adequately sanitize or validate external intents and data payloads before processing them. In the context of mobile application security, Activities are fundamental components that represent single screens with a user interface. When an Activity does not properly restrict who can invoke it or what data it accepts from other applications on the device, it creates a pathway for unauthorized access and execution flows. This specific flaw allows local attackers to craft malicious intents that target this activity, effectively bypassing standard authentication and authorization checks that would normally be required to interact with sensitive payment registration features.
From a technical perspective, this vulnerability is classified as an improper input validation issue, which aligns closely with CWE-20 in the Common Weakness Enumeration taxonomy. The core of the problem lies in the application's failure to verify the integrity and origin of incoming data or intents before executing privileged operations. In Android ecosystems, activities can be exported by default unless explicitly marked otherwise, allowing other applications on the same device to send broadcasts or start these components directly. By exploiting this lack of validation, an attacker can supply arbitrary parameters that manipulate the application's state machine. This manipulation enables the launching of subsequent activities within the Samsung Checkout environment with elevated privileges associated with the checkout process. The attacker does not need physical access to unlock the phone but rather requires local execution capability on the device, which is a common threat model for mobile malware or malicious companion applications installed by users from untrusted sources.
The operational impact of this vulnerability is significant due to the sensitive nature of the data involved. Samsung Checkout handles payment credentials and personal identification information essential for completing transactions without requiring full account creation. If an attacker can launch arbitrary activities with checkout privileges, they may be able to bypass security gates that protect these financial operations. This could lead to unauthorized registration of credit cards under a victim's profile or manipulation of the checkout flow to facilitate fraudulent purchases. Furthermore, because the attack leverages legitimate application components, it may evade basic signature-based detection mechanisms used by some mobile security solutions. The ability to execute arbitrary code within the context of a trusted payment app increases the potential for data exfiltration and financial fraud, posing a direct risk to consumer assets and trust in digital commerce platforms.
To mitigate this vulnerability, developers must implement strict input validation protocols for all exported activities and services. This includes verifying that incoming intents originate from trusted sources by checking package signatures or using explicit intent components rather than implicit ones where possible. Additionally, the GuestCreditCardRegisterActivity should be explicitly marked as non-exported in the AndroidManifest.xml file if it is not intended to be invoked by other applications on the device. Implementing robust authentication checks before allowing access to sensitive financial modules ensures that only authorized users can trigger these operations. For end-users and administrators of devices running affected versions, immediate action involves updating the Samsung Checkout application to version 5.1.03.1 or later, where this input validation flaw has been addressed. Regularly monitoring for security patches from vendors is essential to maintain a secure posture against such local privilege escalation techniques that exploit weak component protection standards.