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Authentication Bypass via bad TOTP + password checks

Critical
emrysal published GHSA-9r3w-4j8q-pw98 Dec 3, 2025

Package

No package listed

Affected versions

<= 5.9.7

Patched versions

5.9.8

Description

Summary

A flaw in the login credentials provider allows an attacker to bypass password verification when a TOTP code is provided, potentially gaining unauthorized access to user accounts. This issue exists due to problematic conditional logic in the authentication flow.

Details

The vulnerability resides in the authorize() function within the credentials provider, specifically in the file packages/features/auth/lib/next-auth-options.ts. The critical flaw is in the authentication logic at lines 179-187, where password verification is skipped if a TOTP code is provided, even if other conditions are met. This leads to two distinct issues:

Scenario 1 - Bypass for Non-2FA Users

When an attacker submits a non-empty value for the totpCode field, password verification is skipped, as the logic evaluates to false when the totpCode is present. This scenario affects users who do not have 2FA enabled (the majority), allowing attackers to bypass both password and TOTP verification. The function then improperly proceeds to authenticate the user without further checks.

Scenario 2 - Reduced Security for 2FA Users

Even for users who have 2FA enabled, the presence of a totpCode causes the function to bypass password verification, reducing the security of the multi-factor authentication process. The TOTP code is validated, but without the password factor, leaving the account vulnerable to compromise if the TOTP code is known.

Vulnerable Code
packages/features/auth/lib/next-auth-options.ts:175-243

      if (!user.password?.hash && user.identityProvider == IdentityProvider.CAL) {
        throw new Error(ErrorCode.IncorrectEmailPassword);
      }

      if (user.password?.hash && !credentials.totpCode) {
        const isCorrectPassword = await verifyPassword(credentials.password, user.password.hash);
        if (!isCorrectPassword) {
          throw new Error(ErrorCode.IncorrectEmailPassword);
        }
      }

      if (user.twoFactorEnabled && credentials.backupCode) {
        ...
      } else if (user.twoFactorEnabled) {
        if (!credentials.totpCode) {
          throw new Error(ErrorCode.SecondFactorRequired);
        }
        const isValidToken = totpAuthenticatorCheck(credentials.totpCode, secret);
        if (!isValidToken) {
          throw new Error(ErrorCode.IncorrectTwoFactorCode);
        }
      }

Potential Attack Method

In certain cases, simply providing a totpCode alongside the victim's email address could lead to unauthorized access, bypassing the password check entirely. The presence of this code, even if incorrect, can allow attackers to access accounts that don't have 2FA or bypass the password check for 2FA users.

Impact

This flaw could result in unauthorized access to sensitive user data, including calendars, meeting links, and personal information. For users without 2FA, attackers could gain access simply by knowing the victim's email address, making the attack easier to execute. Even for users with 2FA enabled, the compromised system allows attackers to bypass one factor of authentication, weakening security. Additionally, the flaw could be exploited to perform user enumeration and impersonation, allowing attackers to gain access to any account if they have sufficient privileges.

By modifying the system’s authentication flow to enforce proper verification of both the password and the TOTP code (if applicable), this vulnerability can be mitigated.

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality High
Integrity High
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:N

CVE ID

CVE-2025-66489

Weaknesses

Incorrect Implementation of Authentication Algorithm

The requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect. Learn more on MITRE.

Credits