SMS verification codes on mobile terminals carry several security risks, primarily due to the vulnerabilities in the SMS channel and mobile device ecosystems. Below are the key risks along with examples:
SIM Swapping Attacks
Attackers trick mobile carriers into transferring a victim's phone number to a new SIM card under their control. Once successful, they receive the SMS verification codes intended for the victim.
Example: A hacker convinces a carrier's support team (using social engineering) that they are the legitimate account holder, then receives banking app login codes sent via SMS.
Malicious Apps with SMS Permissions
Apps installed on a device may request access to SMS messages and silently intercept verification codes.
Example: A seemingly harmless game app requests SMS permissions and forwards one-time passwords (OTPs) to an attacker’s server.
Phishing and Social Engineering
Users may be tricked into revealing SMS codes through fake websites or fraudulent customer support calls.
Example: A phishing email mimics a bank’s login page, asking users to enter their credentials and input the SMS code they receive—directly handing over access to attackers.
Network Interception (SS7 Vulnerabilities)
The Signaling System No. 7 (SS7) protocol, used by telecom networks, has known flaws that allow attackers to redirect SMS messages.
Example: Hackers exploit SS7 weaknesses to intercept SMS codes sent to a target’s phone number, even without physical access to the device.
Device Compromise (Malware)
Malware installed on a smartphone can read incoming SMS messages, including verification codes.
Example: Spyware like Pegasus can monitor SMS traffic, capturing codes for two-factor authentication (2FA).
To reduce risks, consider using app-based authenticators (e.g., Tencent Cloud SMS Verification with additional security layers) or push-based authentication instead of SMS. For critical services, enforce multi-factor authentication (MFA) with biometrics or hardware security keys. Tencent Cloud provides SMS verification services with fraud detection mechanisms to help identify suspicious activities, such as unusual login locations or rapid code requests. Additionally, educating users about phishing and recommending device security best practices (e.g., avoiding unknown apps) can further enhance protection.