Compliance Impact

CVE-2026-49841 is a critical heap buffer overflow vulnerability that can lead to denial of service, information disclosure, and remote code execution in FreeSWITCH's mod_verto module.

Such impacts can compromise the confidentiality, integrity, and availability of data processed by affected systems.

Therefore, if FreeSWITCH is used in environments subject to regulations like GDPR or HIPAA, this vulnerability could lead to non-compliance due to potential unauthorized data access or service disruption.

Mitigating the vulnerability by applying the patch or workarounds is essential to maintain compliance with these standards.

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Executive Summary

CVE-2026-49841 is a critical heap buffer overflow vulnerability in the FreeSWITCH mod_verto module. The module allocates a fixed 2 MiB buffer for HTTP POST requests with application/x-www-form-urlencoded content but accepts a Content-Length header of nearly 10 MiB. This mismatch allows an attacker to send up to 8 MiB of data beyond the allocated buffer, causing a heap overflow before HTTP basic authentication is performed.

The vulnerability is exploitable remotely without credentials or prior interaction and affects systems configured with a <vhost> in the verto profile, typically used for serving files or web interfaces.

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Impact Analysis

This vulnerability can lead to several severe impacts including reliable denial of service, possible information disclosure by corrupting adjacent heap allocations, and plausible remote code execution since the attacker controls the overflow contents.

Because the overflow occurs before authentication, an attacker can exploit it remotely without any credentials, making it highly dangerous.

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Detection Guidance

This vulnerability can be detected by monitoring HTTP POST requests to the FreeSWITCH mod_verto module, specifically those targeting the default listener ports 8081 (plaintext) and 8082 (TLS). Anomalously large Content-Length headers close to 10 MiB with application/x-www-form-urlencoded content type may indicate an attempt to exploit the heap overflow.

Network detection can involve capturing and inspecting HTTP traffic for oversized POST requests to these ports.

Suggested commands for detection include using packet capture tools like tcpdump or tshark to filter such traffic:

• tcpdump -i <interface> 'tcp port 8081 or tcp port 8082 and tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504f5354' -w capture.pcap
• tshark -r capture.pcap -Y 'http.request.method == "POST" and http.content_length > 2000000 and http.content_type == "application/x-www-form-urlencoded"'

Additionally, reviewing FreeSWITCH logs for crashes or abnormal behavior related to mod_verto may help identify exploitation attempts.

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Mitigation Strategies

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

You can also remove any <vhost> entries in the verto profile configuration to disable the HTTP request handler that is vulnerable.

Alternatively, disabling the mod_verto module entirely will prevent exploitation.

Ultimately, upgrading FreeSWITCH to version 1.11.1 or later, where the vulnerability is patched by resizing the body buffer allocation to match the Content-Length header, is the recommended permanent fix.

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