CVE-2026-48683

Vulnerability

An out-of-bounds read vulnerability exists in FastNetMon Community Edition through version 1.2.9 within the NetFlow v9 data flowset processor. In src/netflow_plugin/netflow_v9_collector.cpp, the Data template branch (lines 1695-1702) iterates over flow records without performing a per-iteration bounds check against the packet end pointer, unlike the Options template branch which includes a proper check. Template definitions are received from network peers via unauthenticated UDP, allowing an attacker to supply crafted templates that cause the parser to read beyond the packet buffer [1].

Exploitation

An attacker can exploit this vulnerability by sending a crafted NetFlow v9 UDP packet (default port 2055) containing a malicious template definition followed by a data flowset that references that template. No authentication or prior access is required; the attacker only needs network connectivity to the target. The missing bounds check in the Data branch allows the parser to read out-of-bounds memory on each iteration of the inner loop, leading to memory disclosure or crash [1].

Impact

Successful exploitation results in an out-of-bounds read that can leak sensitive memory contents (e.g., other data in the heap) or cause a denial of service via application crash. The vulnerability affects confidentiality and availability, with no privilege escalation required. The attacker gains no direct code execution but may obtain information useful for further attacks [1].

Mitigation

As of the publication date, no patched version has been released. FastNetMon LTD was notified on April 25, 2026 [1]. Until a fix is available, administrators can mitigate risk by restricting UDP access to the NetFlow collection port (default 2055) to trusted sources only, or by disabling NetFlow v9 support if not required. The vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.