CVE-2020-8289 in Backblaze
Summary
by MITRE • 12/27/2020
Backblaze for Windows before 7.0.1.433 and Backblaze for macOS before 7.0.1.434 suffer from improper certificate validation in `bztransmit` helper due to hardcoded whitelist of strings in URLs where validation is disabled leading to possible remote code execution via client update functionality.
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Analysis
by VulDB Data Team • 12/27/2020
The vulnerability in Backblaze for Windows versions prior to 7.0.1.433 and Backblaze for macOS versions prior to 7.0.1.434 represents a critical security flaw in the certificate validation mechanism of the bztransmit helper application. This issue stems from a hardcoded whitelist of URL string patterns where SSL/TLS certificate validation is deliberately disabled, creating a pathway for malicious actors to exploit the client update functionality. The flaw exists within the software's trust model implementation, specifically targeting the verification process that should ensure secure communication between the backup client and Backblaze servers.
The technical implementation of this vulnerability involves hardcoded string matching logic within the bztransmit helper component that bypasses certificate validation for specific URL patterns. When the backup client attempts to download updates or communicate with backend services, it encounters these predefined URL strings in its whitelist and automatically disables security checks without proper verification. This hardcoded approach creates a persistent attack surface where adversaries can manipulate network traffic to match these whitelisted patterns, effectively circumventing the intended security protections.
The operational impact of this vulnerability extends beyond simple certificate validation bypasses, as it enables potential remote code execution through the client update mechanism. Attackers who can intercept or manipulate network traffic between the Backblaze client and servers could craft malicious responses that match the hardcoded whitelist patterns, allowing them to inject arbitrary code into the update process. This threat model aligns with attack techniques described in the mitre ATT&CK framework under T1059 for execution and T1574 for hijacking trusted processes. The vulnerability essentially provides a foothold for attackers to escalate privileges and potentially compromise entire systems through the backup client's update functionality.
This flaw directly relates to CWE-295 which describes improper certificate validation, and CWE-322 which addresses key exchange without entity authentication. The hardcoded nature of the whitelist pattern matching represents a design flaw that violates fundamental security principles of defense in depth and least privilege. Organizations using affected Backblaze versions face significant risk exposure, as the vulnerability could be exploited by threat actors with network access to perform unauthorized code execution on target systems. The update mechanism serves as a critical attack vector since it typically runs with elevated privileges and has direct system access capabilities.
Mitigation strategies should focus on immediate patching of affected versions to 7.0.1.433 for Windows and 7.0.1.434 for macOS, which address the hardcoded whitelist vulnerability by implementing proper certificate validation logic. Network administrators should also consider implementing additional monitoring for unusual update traffic patterns or attempts to match known whitelist patterns. The fix typically involves removing the hardcoded URL string matching and replacing it with dynamic validation mechanisms that properly assess certificate trustworthiness before establishing secure connections. Security teams should review their incident response procedures to account for potential exploitation of this vulnerability during routine backup operations, as the attack could remain undetected while malicious code executes within the legitimate update process.