CVE-2026-48693
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedFastNetMon 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).
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceFastNetMon Community Edition through 1.2.9 uses a predictable file path '/tmp/fastnetmon.dat' that is vulnerable to symlink attacks. The print_screen_contents_into_file() function opens this file with std::ios::trunc without using O_NOFOLLOW or checking for pre-existing symlinks, allowing local attackers to overwrite arbitrary files. Additionally, a logic bug causes chmod() to operate on the wrong path, and umask is set to 0 during daemonization, making all created files world-writable.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 1.2.9CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed FastNetMon versionRun 'fastnetmon --version' or check package manager (dpkg -l | grep fastnetmon, rpm -qi fastnetmon)Affected if Version is 1.2.9 or lower (any version through 1.2.9)
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Verify FastNetMon runs as rootCheck process owner: ps aux | grep fastnetmon or ps -p $(pidof fastnetmon) -o user=Affected if Process runs as root user (required for arbitrary file overwrite as root)
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Detect vulnerable /tmp/fastnetmon.dat usageCheck if /tmp/fastnetmon.dat file exists and is a symlink: ls -la /tmp/fastnetmon.datAffected if File exists and is a symlink pointing to a sensitive location, OR the file is world-writable (ls -la /tmp/fastnetmon.dat shows rw-rw-rw-)
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Check for world-writable files in /tmp created by FastNetMonList files in /tmp owned by fastnetmon or with modified timestamp: ls -la /tmp/ | grep -E '(fastnetmon|fnm)'Affected if Files exist with permissions 777 (rw-rw-rw-) indicating umask=0 vulnerability
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Inspect binary for vulnerable code patternSearch binary for 'fastnetmon.dat' string: strings $(which fastnetmon) 2>/dev/null | grep fastnetmon.datAffected if Binary references /tmp/fastnetmon.dat path (indicating vulnerable code path)
You are affected if FastNetMon Community Edition version 1.2.9 or lower is installed and runs as root, with /tmp/fastnetmon.dat being world-writable or a symlink present.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataImplement O_NOFOLLOW flag when opening files, add symlink detection before file operations, fix the chmod() logic to operate on the correct file_path parameter, and restore the umask after daemonization instead of setting it to 0.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-48693 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-48693 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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