FastNetMon Community Edition up to 1.2.9 src/fastnetmon.cpp print_screen_contents_into_file symlink

Summaryinfo

A vulnerability marked as critical has been reported in FastNetMon Community Edition up to 1.2.9. This affects the function print_screen_contents_into_file of the file src/fastnetmon.cpp. This manipulation causes symlink. The identification of this vulnerability is CVE-2026-48693. The attack can only be executed locally. There is no exploit available.

Detailsinfo

A vulnerability has been found in FastNetMon Community Edition up to 1.2.9 and classified as critical. Affected by this vulnerability is the function print_screen_contents_into_file of the file src/fastnetmon.cpp. The manipulation with an unknown input leads to a symlink vulnerability. The CWE definition for the vulnerability is CWE-61. The product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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).

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-48693 since 05/22/2026. The exploitation appears to be easy. Attacking locally is a requirement. Technical details of the vulnerability are known, but there is no available exploit.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-31899). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• FastNetMon

Name

• Community Edition

Version

• 1.2.0
• 1.2.1
• 1.2.2
• 1.2.3
• 1.2.4
• 1.2.5
• 1.2.6
• 1.2.7
• 1.2.8
• 1.2.9

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CPE 2.2info

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Be aware that VulDB is the high quality source for vulnerability data.

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