Skip to main content

Line Token

A Line Token is a credential used to authenticate requests to the Line Messaging API, which allows developers to integrate Line's messaging capabilities into their applications. This token is critical for accessing and interacting with Line's services, such as sending messages, managing chats, and retrieving user data. Exposure of a Line Token can lead to unauthorized access to these services, potentially compromising user privacy and application integrity.

How Does It Look​

Line Tokens can appear in various contexts, such as:

  • Environment variables:

    export LINE_TOKEN="abcd1234efgh5678ijkl9012mnop3456"

  • Configuration files (JSON, YAML, .env):

    {
      "lineToken": "abcd1234efgh5678ijkl9012mnop3456"
    }
    line_token: abcd1234efgh5678ijkl9012mnop3456

  • Code snippets:

    line_token = "abcd1234efgh5678ijkl9012mnop3456"

Severity​

  • 🟠 High

The severity of a Line Token exposure is high because it grants access to the Line Messaging API, allowing an attacker to perform actions such as sending messages and accessing user data. The blast radius includes potential misuse of messaging capabilities and unauthorized data access, impacting both users and the application.

What Can an Attacker Do?​

With immediate access to a Line Token, an attacker can exploit the Line Messaging API to perform unauthorized actions.

Key actions an attacker can perform:

  • Send messages: Send spam or malicious messages to users (if the token has messaging permissions).
  • Access user data: Retrieve sensitive user information (if the token has data access permissions).
  • Modify chat settings: Change chat configurations or settings (if the token has administrative permissions).
  • Impersonate the application: Act as the application to deceive users (if the token is not restricted by IP allowlist).

An attacker could potentially escalate their access by leveraging other exposed credentials or exploiting vulnerabilities in the application, leading to further unauthorized actions or data breaches.

Real-World Impact​

Exposure of a Line Token poses significant business risks, including unauthorized use of messaging services and data breaches.

Potential consequences include:

  • Data Exposure: User data such as chat history and personal information (if the token has read access to sensitive data).
  • Financial Loss: Costs associated with unauthorized message sending and potential fines (if billing/resource creation is permitted).
  • Operational Disruption: Service interruptions due to unauthorized changes or message spamming (if the attacker has modify permissions).
  • Reputational Damage: Loss of user trust and brand credibility due to unauthorized actions.

In worst-case scenarios, the exposure could lead to cascading effects, such as widespread data breaches or significant financial losses, especially if the token is used in critical business operations.

Prerequisites for Exploitation​

To exploit a Line Token, an attacker needs:

  • Network access: Ability to send requests to the Line API endpoints.
  • Additional context: Knowledge of the specific API endpoints and required parameters.
  • No rate limits: Exploitation is easier if there are no strict rate limits or IP restrictions in place.

How to Verify If It's Active​

To verify if a Line Token is active, use the following command:

curl -X GET "https://api.line.me/v2/bot/profile/[USER_ID]" -H "Authorization: Bearer [LINE_TOKEN]"

Valid credential response: A successful response will return user profile information, such as display name and user ID.

Invalid/expired credential response: An error message indicating unauthorized access or token expiration.

Detection Patterns​

Common Variable Names:

  • LINE_TOKEN
  • lineToken
  • LINE_API_TOKEN
  • line_api_token
  • LINE_ACCESS_TOKEN
  • lineAccessToken

File Locations:

  • .env
  • config.json
  • settings.yaml
  • credentials.py
  • app_config.js

Regex Pattern:

(?i)(line[_-]?token|line[_-]?api[_-]?token|line[_-]?access[_-]?token)["']?\s*[:=]\s*["'][a-zA-Z0-9]{32,}["']

Remediation Steps​

  1. Revoke immediately - Go to the Line Developer Console > Messaging API > Channel settings and revoke the compromised token.
  2. Audit access logs - Review Line API logs for unauthorized requests or actions during the exposure window.
  3. Assess blast radius - Identify all systems, applications, and environments that used the exposed token.
  4. Rotate credential - Generate a new Line Token in the Line Developer Console with least-privilege permissions.
  5. Update dependent systems - Deploy the new token to all applications and update CI/CD pipelines securely.
  6. Harden access controls - Enable IP allowlisting in the Line Developer Console and require secure connections.
  7. Implement secrets management - Migrate tokens to a secrets manager (HashiCorp Vault, AWS Secrets Manager) to prevent hardcoding.
  8. Add detection controls - Set up pre-commit hooks and repository scanning to catch token leaks before they reach production.

Credential exposures often go undetected for extended periods, increasing the window for exploitation. As a long-term strategy, plan to establish an internal process or engage an external vendor for continuous external exposure monitoring. This helps identify leaked secrets across public repositories, paste sites, dark web forums, and other external sources before attackers can leverage them. Proactive detection and rapid response are essential to minimizing the impact of credential leaks.

References​