Summary
Course-tencent-cloud through version 2.0.1 does not sufficiently restrict authentication and verification attempts. An unauthenticated attacker who knows a victim's phone number or email address may repeatedly guess a six-digit code and potentially take over the account.
Course-tencent-cloud through version 2.0.1 does not sufficiently restrict authentication and verification attempts. An unauthenticated attacker who knows a victim's phone number or email address may repeatedly guess a six-digit code and potentially take over the account.
Affected context
The vulnerability occurs in password-reset and login-verification workflows that rely on six-digit SMS or email codes. Risk increases when codes remain valid after use, when repeated guesses are not rate-limited, and when attackers can rotate source IP addresses to avoid network-based controls.
The vulnerability occurs in password-reset and login-verification workflows that rely on six-digit SMS or email codes. Risk increases when codes remain valid after use, when repeated guesses are not rate-limited, and when attackers can rotate source IP addresses to avoid network-based controls.
Exploit preconditions
- Attack surface: Public password-reset and verification endpoints
- Required access: No authenticated access; knowledge of the victim's phone number or email address may be sufficient
- Trigger point: Submission of repeated verification-code guesses
- Why exploitation is possible: Verification codes are not reliably invalidated or protected by effective attempt limits, allowing online brute-force attempts across rotating source addresses
- Attack surface: Public password-reset and verification endpoints
- Required access: No authenticated access; knowledge of the victim's phone number or email address may be sufficient
- Trigger point: Submission of repeated verification-code guesses
- Why exploitation is possible: Verification codes are not reliably invalidated or protected by effective attempt limits, allowing online brute-force attempts across rotating source addresses
Why this happens
The underlying flaw is insufficient enforcement of authentication-attempt restrictions. The application accepts repeated guesses for a short verification code without consistently expiring the code, limiting attempts, or binding verification activity to a controlled session or context. This maps to CWE-307: Improper Restriction of Excessive Authentication Attempts, because the system does not adequately prevent automated guessing of authentication credentials or tokens.
The underlying flaw is insufficient enforcement of authentication-attempt restrictions. The application accepts repeated guesses for a short verification code without consistently expiring the code, limiting attempts, or binding verification activity to a controlled session or context. This maps to CWE-307: Improper Restriction of Excessive Authentication Attempts, because the system does not adequately prevent automated guessing of authentication credentials or tokens.
Potential impact
- An attacker may gain access to a victim's account
- Password-reset protections could be bypassed
- Personal information and application data may be exposed
- Attackers could modify account settings or perform actions as the victim
- Compromised accounts may be used for fraud, abuse, or further intrusion
- An attacker may gain access to a victim's account
- Password-reset protections could be bypassed
- Personal information and application data may be exposed
- Attackers could modify account settings or perform actions as the victim
- Compromised accounts may be used for fraud, abuse, or further intrusion
General mitigation guidance
Mitigation generally focuses on making verification tokens short-lived, single-use, and resistant to guessing.
Common defensive patterns include:
- Enforcing strict per-account, per-token, per-session, and network-aware attempt limits
- Invalidating codes immediately after successful use, expiration, or excessive failed attempts
- Applying progressive delays, temporary lockouts, and risk-based challenge controls
- Binding verification flows to the original reset or login transaction rather than accepting codes in isolation
- Reducing reliance on source IP addresses alone, since attackers may rotate addresses
- Avoiding account-enumeration signals and protecting recovery endpoints with consistent responses
- Applying least privilege to recovery operations and requiring additional verification for sensitive changes
Mitigation generally focuses on making verification tokens short-lived, single-use, and resistant to guessing.
Common defensive patterns include:
- Enforcing strict per-account, per-token, per-session, and network-aware attempt limits
- Invalidating codes immediately after successful use, expiration, or excessive failed attempts
- Applying progressive delays, temporary lockouts, and risk-based challenge controls
- Binding verification flows to the original reset or login transaction rather than accepting codes in isolation
- Reducing reliance on source IP addresses alone, since attackers may rotate addresses
- Avoiding account-enumeration signals and protecting recovery endpoints with consistent responses
- Applying least privilege to recovery operations and requiring additional verification for sensitive changes
How teams detect issues like this
Detection can combine application testing, code review, and runtime monitoring:
- Use static analysis to identify verification handlers without counters, expiration checks, or token invalidation
- Review code for reusable tokens, unlimited retry loops, and controls based only on client-supplied or source-IP data
- Test password-reset and login-verification endpoints for effective limits across accounts, sessions, devices, and changing IP addresses
- Monitor repeated failures, unusual geographic or network changes, high-volume code requests, and successful verification after many guesses
- Enforce API security policies requiring rate limiting, token expiry, single-use semantics, and audit logging
- Automated security testing and code-review tools may help identify missing authentication-attempt controls
Detection can combine application testing, code review, and runtime monitoring:
- Use static analysis to identify verification handlers without counters, expiration checks, or token invalidation
- Review code for reusable tokens, unlimited retry loops, and controls based only on client-supplied or source-IP data
- Test password-reset and login-verification endpoints for effective limits across accounts, sessions, devices, and changing IP addresses
- Monitor repeated failures, unusual geographic or network changes, high-volume code requests, and successful verification after many guesses
- Enforce API security policies requiring rate limiting, token expiry, single-use semantics, and audit logging
- Automated security testing and code-review tools may help identify missing authentication-attempt controls
