Skip to content

Latest commit

 

History

History
52 lines (43 loc) · 6.15 KB

threat-modeling.md

File metadata and controls

52 lines (43 loc) · 6.15 KB

Threat Model Analysis for signalapp/signal-android

Threat: Malicious Attachment Handling

  • Description: An attacker sends a specially crafted attachment (e.g., a malicious image, video, or document) that exploits a vulnerability in Signal's attachment handling code. This leverages a bug within Signal's code for processing attachments.
    • Impact: Potential code execution, information disclosure, or denial of service. Severity depends on the specific vulnerability, but could allow an attacker to compromise the Signal application on the device.
    • Affected Component: org.thoughtcrime.securesms.attachments package and related classes, specifically the code responsible for parsing and displaying different attachment types (e.g., ImageAttachment, VideoAttachment, etc.). Also, any third-party libraries used by Signal itself for media processing (e.g., image decoders).
    • Risk Severity: High (potentially Critical, depending on the vulnerability)
    • Mitigation Strategies:
      • Secure Coding Practices: Rigorous input validation and sanitization of all attachment data within the Signal codebase.
      • Fuzz Testing: Extensive fuzz testing of attachment parsing code within Signal.
      • Memory Safety: Use memory-safe languages or techniques (e.g., Rust) where possible within Signal's codebase.
      • Sandboxing: Isolate attachment processing in a separate process or sandbox (this is a design consideration for the Signal team).
      • Regular Updates: Promptly apply security updates to Signal and any third-party libraries it uses.

Threat: Compromised Backup Key (if backups are enabled)

  • Description: If the user enables Signal backups and chooses a weak passphrase, an attacker could brute-force the passphrase and decrypt the backup, gaining access to the user's message history. This relies on the user's choice, but the implementation of backup encryption is within Signal.
    • Impact: Complete compromise of the user's backed-up message history.
    • Affected Component: org.thoughtcrime.securesms.backup package, specifically the code related to backup creation and restoration within Signal.
    • Risk Severity: High
    • Mitigation Strategies:
      • Strong Passphrase Enforcement: Signal should strongly encourage users to choose strong, unique passphrases for their backups, possibly with minimum complexity requirements.
      • Key Derivation Function (KDF): Signal already uses a strong KDF (e.g., scrypt, Argon2) to make brute-forcing computationally expensive. This should be regularly reviewed and updated as needed.
      • User Education: Signal should clearly educate users about the importance of strong passphrases and the risks of weak backups.
      • Limit Backup Attempts: Implement a mechanism within Signal to limit the number of incorrect backup passphrase attempts (both locally and potentially on the server if backup metadata is stored).

Threat: Exploiting Vulnerabilities in Third-Party Libraries (used by Signal)

  • Description: Signal-Android relies on numerous third-party libraries. An attacker could exploit a vulnerability in one of these libraries used by Signal to compromise Signal's security. This is a vulnerability within Signal's dependency tree.
    • Impact: Varies greatly depending on the vulnerable library and the nature of the vulnerability. Could range from denial of service to arbitrary code execution within the Signal app.
    • Affected Component: Any third-party library used by Signal-Android. Examples include libraries for image processing, networking, cryptography (although core crypto is usually handled by libsignal), etc. This can be found in the build.gradle files of the Signal project.
    • Risk Severity: High (potentially Critical)
    • Mitigation Strategies:
      • Dependency Management: Signal team must use a robust dependency management system (e.g., Gradle) to track and update dependencies.
      • Vulnerability Scanning: Signal team must regularly scan dependencies for known vulnerabilities using tools like OWASP Dependency-Check.
      • Software Bill of Materials (SBOM): Signal team should maintain an SBOM to track all components and their versions.
      • Prompt Updates: Signal team must apply security updates to third-party libraries as soon as they become available.
      • Library Selection: Signal team must carefully vet third-party libraries before including them in the project, choosing libraries with a strong security track record.

Threat: Registration Lock Bypass (within Signal's implementation)

  • Description: An attacker attempts to bypass the Registration Lock feature, which requires a PIN to register the user's phone number on a new device. This focuses on exploiting vulnerabilities in Signal's implementation of the PIN verification or recovery mechanism, not social engineering.
    • Impact: The attacker could register the user's phone number on their own device, effectively hijacking the account.
    • Affected Component: org.thoughtcrime.securesms.registration.RegistrationLock and related classes, as well as the server-side components that handle registration lock verification within Signal's infrastructure.
    • Risk Severity: High
    • Mitigation Strategies:
      • Strong PIN Enforcement: Signal should enforce strong, non-guessable PINs.
      • Rate Limiting: Signal's server-side components must implement strict rate limiting on PIN entry attempts.
      • Secure PIN Recovery: If a PIN recovery mechanism is provided by Signal, it must be highly secure and resistant to attacks. The implementation details are critical.
      • Account Activity Monitoring: Signal should notify users of any attempts to register their number on a new device.