Vulnerability · Published May 26, 2026 · Assigned by mitre
CVE-2026-48693
Medium 5.5
In plain English
A medium-severity security flaw 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 0.1% (higher than 2% of all known vulnerabilities).
Official description
FastNetMon Community Edition through 1.2.9 is vulnerable to a local symlink attack via predictable file paths in /tmp. The statistics file path defaults to '/tmp/fastnetmon.dat' (src/fastnetmon.cpp line 159). The print_screen_contents_into_file() function (src/fastnetmon_logic.cpp line 2186) opens this path with std::ios::trunc without checking for symlinks or using O_NOFOLLOW. Additionally, the chmod() call on line 2190 always operates on cli_stats_file_path regardless of which file_path parameter was passed (a bug that applies wrong permissions), and the umask is set to 0 during daemonization (src/fastnetmon.cpp line 1821), making all created files world-writable. A local attacker can exploit this to overwrite arbitrary files as the FastNetMon process user (typically root).
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | fastnetmon | no fix listed | DEBIAN-CVE-2026-48693 |
| Debian:13 | fastnetmon | no fix listed | DEBIAN-CVE-2026-48693 |
| Debian:14 | fastnetmon | no fix listed | DEBIAN-CVE-2026-48693 |
| Ubuntu:25.10 | fastnetmon | no fix listed | UBUNTU-CVE-2026-48693 |
| Ubuntu:26.10 | fastnetmon | no fix listed | UBUNTU-CVE-2026-48693 |
Affected products (as reported)
Weakness: CWE-59 · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N