Buffer overflow in Pavel-Odintsov Fastnetmon
CVE-2026-48689
FastNetMon Community Edition through 1.2.9 contains an off-by-one heap-based buffer overflow in the dynamic_binary_buffer_t class (src/dynamic_binary_buffer.hpp). Five methods (append_dynamic_buffer, append_data_as_pointer, append_data_as_object_ptr, memcpy_from_ptr, memcpy_from_object_ptr) use an incorrect bounds check of the form 'if (offset + length > maximum_internal_storage_size + 1)' instead of the correct 'if (offset + length > maximum_internal_storage_size)'. This allows writing exactly one byte past the end of the heap-allocated buffer. The class is used pervasively in BGP message encoding/decoding, NetFlow template processing, and Flow Spec NLRI construction. An attacker who can send network traffic (NetFlow, sFlow, IPFIX, or BGP) to a FastNetMon instance can trigger this overflow, potentially achieving arbitrary code execution by corrupting heap metadata. Notably, the append_byte() method uses the correct bounds check, confirming the inconsistency.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.009 (59.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 59.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.007 · newest: 0.009 · change: +0.002
Affected products
Weakness classification (CWE)
References
- github.com/pavel-odintsov/fastnetmon (Product)
- github.com/pavel-odintsov/fastnetmon/blob/master/src/dynamic_binary_buffer.hpp (Product)
- lorikeetsecurity.com/blog/fastnetmon-cve-2026-48689-dynamic-buffer-off-by-one (Exploit, Third Party Advisory)
Frequently asked questions
- What is CVE-2026-48689?
- CVE-2026-48689 is a critical-severity vulnerability in Pavel-Odintsov Fastnetmon, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-05-26.
- How severe is CVE-2026-48689?
- Critical severity. CVSS v3 base score is 9.8 out of 10.