Vulnerability · Published May 26, 2026 · Assigned by mitre
CVE-2026-48691
High 7.3
In plain English
A high-severity integer overflow in the fastnetmon package (Debian). There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 24% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
FastNetMon Community Edition through 1.2.9 contains an integer overflow in the BGP AS_PATH attribute encoder. In src/bgp_protocol.hpp, the IPv4UnicastAnnounce::get_attributes() function computes attribute_length as 'sizeof(bgp_as_path_segment_element_t) + this->as_path_asns.size() * sizeof(uint32_t)' and stores it in a uint8_t field (line 600-605). Since uint8_t can only hold values 0-255, an AS_PATH containing more than 63 ASNs (2 + 64*4 = 258 > 255) causes silent truncation. The truncated length is used for buffer sizing, while the actual data written is the full untruncated amount, resulting in a heap buffer overflow. Similarly, the path_segment_length field at line 621 is also uint8_t, truncating with more than 255 ASNs.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | fastnetmon | no fix listed | DEBIAN-CVE-2026-48691 |
| Debian:13 | fastnetmon | 1.2.9-0+deb13u1 | DEBIAN-CVE-2026-48691 |
| Debian:14 | fastnetmon | 1.2.9-1 | DEBIAN-CVE-2026-48691 |
| Ubuntu:25.10 | fastnetmon | no fix listed | UBUNTU-CVE-2026-48691 |
| Ubuntu:26.10 | fastnetmon | no fix listed | UBUNTU-CVE-2026-48691 |
Affected products (as reported)
Weakness: CWE-190, CWE-122 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L