Executive brief
FreeSWITCH, a software-based telecommunications platform, contains a flaw in its WebSocket communication module. An unauthenticated attacker can send a small, specially crafted request that forces the server to respond with massive amounts of data (up to 20 GB). This can saturate the server's internet connection and exhaust system resources, leading to a total service outage for legitimate users.
Technical details
A vulnerability exists in the mod_verto module's WebSocket frame loop where speed-test protocol commands (#SPU, #SPB, #SPE) are processed before authentication. The payload size in the #SPU command is parsed using atoi() without upper-bound validation, allowing an unauthenticated peer to request up to INT_MAX bytes. The server responds by writing approximately 10 times the requested size back to the client, potentially generating 20 GB of outbound traffic from a single small request. This results in significant bandwidth amplification and resource exhaustion. The issue is fixed in version 1.11.1 by requiring authentication for speed-test commands and capping the maximum size to 10 MiB.
Affected products
- SignalWire FreeSWITCH < 1.11.1
Timeline
- 2026-05-26: patched: Version 1.11.1 released
- 2026-06-03: advisory: GitHub Security Advisory published
- 2026-06-09: disclosed: CVE published to NVD