Overview
CVE-2025-6599 is a medium severity vulnerability affecting the web server of Zyxel DX3301-T0 routers. This vulnerability allows an attacker to perform Slowloris-style denial-of-service (DoS) attacks, potentially disrupting access to the web management interface and legitimate HTTP requests.
Technical Details
The vulnerability stems from an uncontrolled resource consumption issue within the Zyxel DX3301-T0’s web server. Specifically, the web server fails to properly manage concurrent HTTP connections, making it susceptible to Slowloris attacks. Slowloris exploits this weakness by sending partial HTTP requests and keeping the connections open for extended periods. By sending a large number of these incomplete requests, an attacker can exhaust the server’s resources, preventing legitimate users from accessing the web interface.
Affected firmware versions include 5.50(ABVY.6.3)C0 and earlier.
CVSS Analysis
The Common Vulnerability Scoring System (CVSS) score for CVE-2025-6599 is 5.3 (MEDIUM). This score reflects the potential impact of a successful attack, which can lead to a partial disruption of service. The CVSS vector string may vary based on the calculator, but generally considers factors like network attack vector, low attack complexity, no privileges required, no user interaction, limited impact on availability, and no impact on confidentiality or integrity.
Possible Impact
A successful Slowloris attack exploiting CVE-2025-6599 can lead to the following impacts:
- Temporary denial-of-service, blocking legitimate HTTP requests.
- Partial disruption of access to the web management interface, making it difficult for administrators to manage the router.
- Degraded performance for users relying on web-based services.
- Other networking services remain unaffected.
Mitigation or Patch Steps
The primary mitigation step is to update the Zyxel DX3301-T0 router to a firmware version that addresses this vulnerability. Check the Zyxel support website for the latest firmware release.
- Visit the Zyxel Download Library.
- Search for “DX3301-T0”.
- Download and install the latest firmware version available.
If a firmware update is not immediately available, consider implementing temporary workarounds, such as configuring intrusion detection systems (IDS) or intrusion prevention systems (IPS) to detect and block Slowloris attacks. Rate limiting on the web server might also help reduce the impact.
