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attack-surface.md

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Attack Surface Analysis for borgbackup/borg

Attack Surface: Compromised Repository Access Credentials (Passphrase/Key)

  • Description: Unauthorized access to the Borg repository due to compromised passphrase or key file, bypassing Borg's encryption and access control.
  • Borg Contribution: Borg's security model fundamentally relies on the secrecy of the passphrase or key file to protect backup data. Compromise directly defeats this core security mechanism.
  • Example: A developer accidentally commits a file containing the Borg repository passphrase to a public Git repository. An attacker finds this passphrase, connects to the Borg repository, and downloads all encrypted backups.
  • Impact: Data breach, complete loss of backup confidentiality, data manipulation (attacker can modify or delete backups), denial of service (by deleting backups).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Developers/Users:
      • Strong Passphrases/Key Files: Mandate and enforce the use of strong, randomly generated passphrases or key files for repository encryption.
      • Secure Secret Management: Utilize dedicated and secure secret management solutions (e.g., HashiCorp Vault, cloud provider key management services) to store and manage Borg repository passphrases and keys.
      • Principle of Least Privilege for Credentials: Restrict access to Borg repository credentials to only essential personnel and automated processes.
      • Regular Key Rotation: Implement a policy for periodic rotation of Borg repository passphrases or keys to limit the window of opportunity for compromised credentials.

Attack Surface: Borg Client Binary Compromise

  • Description: A malicious actor compromises the Borg client binary, allowing them to manipulate the backup process and potentially exfiltrate or corrupt backup data.
  • Borg Contribution: The Borg client is the trusted component responsible for all security-sensitive operations like encryption and data handling. A compromised client becomes a powerful attack vector against the entire backup system.
  • Example: An attacker compromises the build pipeline used to create Borg client binaries and injects malware. Users unknowingly download and use this compromised binary, which silently exfiltrates backup data to an attacker-controlled server during backup jobs.
  • Impact: Data breach (exfiltration of backup data), data manipulation (injection of malware into backups, data corruption), data loss (selective exclusion of critical data from backups), complete compromise of backup integrity and confidentiality.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers/Users:
      • Official and Verified Sources: Download Borg client binaries exclusively from official and verified sources like the official Borg GitHub releases or trusted operating system package repositories.
      • Binary Verification: Implement and enforce verification of downloaded Borg client binaries using cryptographic signatures provided by the Borg project.
      • Secure Software Supply Chain: For developers distributing Borg, implement robust security measures throughout the software supply chain to prevent binary compromise.
      • Endpoint Security: Deploy and maintain strong endpoint security measures (e.g., EDR, anti-malware) on systems running the Borg client to detect and prevent malicious modifications.

Attack Surface: Borg Serve Service Vulnerabilities (If Used for Remote Access)

  • Description: Exploitation of security vulnerabilities within the borg serve service, if used to expose Borg repositories over a network, leading to unauthorized repository access or server compromise.
  • Borg Contribution: borg serve is a network service component of Borg. Vulnerabilities in this service directly expose the Borg repository to network-based attacks, bypassing client-side protections.
  • Example: A remote code execution vulnerability is discovered in borg serve. An attacker exploits this vulnerability to gain shell access to the server running borg serve, allowing them to directly access and manipulate all Borg repositories served by that instance.
  • Impact: Remote repository access compromise, server compromise, data breach, data manipulation, denial of service against the borg serve service and potentially other services on the same server.
  • Risk Severity: High (if borg serve is exposed to a network)
  • Mitigation Strategies:
    • Developers/Users:
      • Minimize borg serve Exposure: Avoid exposing borg serve directly to the public internet. If remote access is necessary, restrict access using VPNs, firewalls, and network segmentation.
      • Prefer SSH Tunneling: Prioritize using SSH tunneling for remote Borg repository access instead of directly exposing borg serve.
      • Regular Updates and Patching: Maintain borg serve and the underlying operating system with the latest security patches to mitigate known vulnerabilities.
      • Security Audits and Penetration Testing: Conduct regular security audits and penetration testing specifically targeting the borg serve service and its deployment environment.
      • Disable Unnecessary Features: Disable any unnecessary features or functionalities of borg serve to reduce the attack surface.

Attack Surface: Weak Passphrase Leading to Brute-Force Decryption

  • Description: Using a weak passphrase for repository encryption makes the backups vulnerable to offline brute-force attacks, even if Borg's encryption algorithms are strong.
  • Borg Contribution: While Borg uses strong encryption, the passphrase strength is a critical factor. A weak passphrase negates the strength of the encryption, directly impacting Borg's security effectiveness.
  • Example: A user sets a simple and short passphrase for their Borg repository. An attacker obtains a copy of the encrypted repository data. Using specialized password cracking tools and techniques, they successfully brute-force the weak passphrase and decrypt the backups offline.
  • Impact: Data breach, unauthorized access to backups, loss of backup confidentiality.
  • Risk Severity: High (if weak passphrases are permitted)
  • Mitigation Strategies:
    • Developers/Users:
      • Enforce Strong Passphrase Policies: Implement and enforce policies requiring strong, complex, and sufficiently long passphrases for Borg repositories.
      • Passphrase Strength Validation: Integrate passphrase strength validation tools or libraries into systems that manage Borg passphrase creation to guide users towards strong choices.
      • Key File Preference: Encourage and promote the use of randomly generated key files instead of manually created passphrases, as key files are inherently stronger.
      • Security Awareness Training: Regularly educate users about the critical importance of strong passphrases for backup security and the risks associated with weak passphrases.

Attack Surface: Vulnerabilities in Critical Borg Dependencies Leading to Code Execution

  • Description: Security vulnerabilities in critical third-party libraries used by Borg, specifically those that can lead to arbitrary code execution, can be exploited through Borg.
  • Borg Contribution: Borg relies on external libraries for core functionalities. A critical vulnerability in a dependency that allows code execution directly impacts Borg's security and can be exploited via malicious backup operations or data processing.
  • Example: A buffer overflow vulnerability is discovered in a compression library used by Borg. An attacker crafts a malicious archive that, when processed by Borg during a backup or restore operation, triggers the buffer overflow, leading to arbitrary code execution on the system running the Borg client.
  • Impact: Remote or local code execution on systems running Borg, potentially leading to data breach, data manipulation, denial of service, privilege escalation, and full system compromise.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developers/Users:
      • Proactive Dependency Monitoring: Implement continuous monitoring of Borg's dependencies for newly disclosed vulnerabilities using vulnerability scanning tools and security advisories.
      • Rapid Patching and Updates: Establish a process for promptly patching or updating Borg and its dependencies upon the discovery and release of fixes for critical vulnerabilities.
      • Software Composition Analysis (SCA): For developers packaging or deploying Borg, integrate SCA tools into development and deployment pipelines to automatically identify and track dependency vulnerabilities.
      • Dependency Isolation (if feasible): Explore techniques to isolate Borg's dependencies to limit the potential impact of a compromised dependency (e.g., containerization, sandboxing).