Compliance Impact

The vulnerability in FreeSWITCH's mod_verto module allows an unauthenticated attacker to cause a denial of service by exhausting server resources through bandwidth amplification. While the CVE description and resources do not explicitly mention compliance with standards such as GDPR or HIPAA, the resulting denial of service and potential service unavailability could indirectly impact compliance with regulations that require maintaining availability and reliability of services.

Specifically, the high impact on availability (CVSS score 7.5, with a high impact on availability) could violate requirements in standards that mandate continuous service availability and protection against denial of service attacks. However, there is no direct information linking this vulnerability to data confidentiality or integrity breaches relevant to GDPR or HIPAA.

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Executive Summary

CVE-2026-49842 is a high-severity vulnerability in FreeSWITCH versions 1.11.0 and earlier, specifically in the mod_verto WebSocket module. The vulnerability arises because the mod_verto's WebSocket frame loop intercepts certain speed-test protocol commands (prefixed with #, such as #SPU, #SPB, #SPE) before any authentication is performed.

The server parses the declared payload size in the #SPU command using the atoi() function, which only rejects non-positive values. This allows an unauthenticated attacker to request an extremely large payload size, up to INT_MAX bytes.

During the download phase, the server responds by writing roughly ten times the requested size back to the attacker, potentially sending about 20 GB per request. This results in a strong outbound bandwidth amplification.

The speed-test functionality is enabled unconditionally and runs before authentication, so no credentials or prior interaction are needed to exploit this issue.

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Impact Analysis

This vulnerability can be exploited by an unauthenticated attacker to cause a denial of service (DoS) condition on the affected FreeSWITCH server.

By sending specially crafted speed-test protocol frames, the attacker can cause the server to send a massive amount of outbound data—up to 20 GB per request—resulting in strong bandwidth amplification.

This can saturate the server's outbound network link, exhaust socket and thread resources, and ultimately deny service to legitimate users.

The attack requires no authentication and can be performed remotely over the network, making it easy to execute.

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Detection Guidance

This vulnerability can be detected by monitoring for unusual or excessive outbound bandwidth usage on the FreeSWITCH server, especially on ports 8081 (plaintext) and 8082 (TLS) where the mod_verto WebSocket listener operates.

Specifically, look for WebSocket frames containing the #-prefixed speed-test protocol commands such as #SPU, #SPB, or #SPE being sent before any authentication.

Network detection commands could include using packet capture tools like tcpdump or Wireshark to filter WebSocket traffic on these ports and inspect for these specific commands.

• tcpdump -i <interface> -A port 8081 or port 8082 | grep '#SPU\|#SPB\|#SPE'
• Use WebSocket inspection tools or scripts to parse incoming frames on mod_verto ports for the presence of speed-test commands before authentication.

Additionally, monitoring server logs for unusually large outbound data transfers correlated with unauthenticated WebSocket connections can help identify exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the mod_verto WebSocket listener ports (8081 and 8082) to trusted networks only.

If mod_verto is not in use, disabling the module entirely is recommended to eliminate the attack surface.

Upgrading FreeSWITCH to version 1.11.1 or later is the definitive fix, as it requires authentication before processing speed-test frames and caps the payload size to 10 MiB.

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