Critical DrayTek Router Vulnerabilities Expose Devices to RCE Attacks

A recent security analysis of Draytek Vigor routers has uncovered severe vulnerabilities that could allow attackers to hijack devices, execute arbitrary code, and bypass critical security controls.

These findings, disclosed by researchers at DEFCON 32 HHV and Ekoparty 2024, highlight systemic risks in widely used small office/home office (SOHO) routers due to outdated firmware, weak authentication mechanisms, and insecure update processes.

Below, we break down the technical details and implications of these flaws.

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Authentication Bypasses and Insecure Code Execution

Draytek routers exhibited multiple critical authentication weaknesses.

The CVE-2024-41335 vulnerability leverages non-constant time password comparisons using strcmp and memcmp, enabling timing attacks to extract credentials.

Compounding this, CVE-2024-41336 reveals plaintext password storage in memory, allowing physical or memory-dumping attacks.

Researchers also identified a predictable 2FA code generation flaw (unassigned CVE), where codes are derived from the router’s uptime.

Attackers could force a reboot (via CVE-2024-41338, a DHCP-triggered denial-of-service flaw) and calculate new codes to bypass two-factor authentication.

Kernel-level risks were flagged in CVE-2024-41339 and CVE-2024-41340, which permit arbitrary kernel module uploads via CGI endpoints and unvalidated SSL certificate checks for APP Enforcement updates.

These allow attackers to install malicious modules, achieving persistent root access.

Memory Corruption Vulnerabilities and Remote Exploitation

Two high-severity remote code execution (RCE) flaws—CVE-2024-51138 and CVE-2024-51139—exploit memory corruption.

The TR069 STUN server’s stack-based buffer overflow (CVE-2024-51138) enables unauthenticated attackers to execute code via malformed URLs.

Meanwhile, the CGI POST handler’s integer overflow (CVE-2024-51139) corrupts heap memory by mishandling Content-Length headers, leading to RCE.

These vulnerabilities are particularly dangerous for routers exposed to WAN traffic, as they require no authentication and can be exploited remotely.

Affected Firmware and Mitigation Strategies

The vulnerabilities impact multiple Draytek models, including Vigor165, Vigor2860, and Vigor3912 series.

Firmware versions vary by CVE:

• CVE-2024-41334 to CVE-2024-41338: Affects Vigor2860/2925 (pre-3.9.7) and Vigor2133/2762 (pre-3.9.8).
• CVE-2024-51138/51139: Impacts Vigor2620 (pre-3.9.9.1) and Vigor2865 (pre-4.4.5.8).

Draytek has released patches for most flaws, but SOHO users often delay updates, leaving networks exposed.

Researchers urge immediate firmware upgrades and disabling unused services like TR069 or STUN.

Network administrators should also enforce HTTPS for management interfaces and monitor for unexpected kernel module installations.

These findings underscore the fragile state of SOHO router security, where proprietary firmware and infrequent updates create fertile ground for attackers.

As Draytek routers often serve as entry points for larger networks, unpatched devices risk becoming pivot points for lateral movement.

Researchers plan to release technical deep dives on CVE-2024-51138 and CVE-2024-51139 in upcoming posts, emphasizing the need for proactive defense in an era of increasingly sophisticated network intrusions.

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