CVE-2026-48693

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).

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Severity score breakdown

CVSS version: CVSS v3.0

References

• MITRE
• NVD
• Launchpad
• Debian

Other references

• https://www.cve.org/CVERecord?id=CVE-2026-48693
• https://lorikeetsecurity.com/blog/fastnetmon-cve-2026-48693-symlink-tmp
• https://github.com/pavel-odintsov/fastnetmon
• https://github.com/pavel-odintsov/fastnetmon/blob/master/src/fastnetmon.cpp
• https://github.com/pavel-odintsov/fastnetmon/blob/master/src/fastnetmon_logic.cpp