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Link Following (Symlink)Weakness · CWE-59

CVE-2026-20161

MEDIUM · 5.5 CVSS v3.1 Published 2026-04-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
57/100
Remediation priority · Elevated
Zero-click

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 · unedited
A vulnerability in the CLI of Cisco ThousandEyes Enterprise Agent could allow an authenticated, local attacker with low privileges to overwrite arbitrary files on the local system of an affected device. This vulnerability is due to improper access controls on files that are on the local file system of an affected device. An attacker could exploit this vulnerability by placing a symbolic link in a specific location on the local file system. A successful exploit could allow the attacker to bypass file system permissions and overwrite arbitrary files on the affected device.

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 · moderate confidence

A low-privilege authenticated local attacker can exploit improper access controls in the Cisco ThousandEyes Enterprise Agent CLI by placing a symbolic link in a specific location on the local file system, allowing them to bypass file permissions and overwrite arbitrary files on the affected device.

MitigationApply Cisco's patch when available; until then, restrict local CLI access to trusted low-privilege users and monitor for suspicious symbolic link creation in the agent's directories.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify if ThousandEyes Enterprise Agent is installed
    Check for the agent process: run 'ps aux | grep -i thousandeyes' or 'ps aux | grep te-agent'. Also look for installation directories such as /opt/thousandeyes, /usr/share/thousandeyes, or the binary location via 'which te-agent'
    Affected if The agent process is running or the te-agent binary exists on the system
  2. Determine the installed version
    Run 'te-agent --version' if the binary is available, or check the agent installation directory for a VERSION file. On Linux, use package queries like 'rpm -q thousandeyes-agent' or 'dpkg -l thousandeyes-agent' to retrieve the installed version string
    Affected if The installed version matches the affected range or cannot be determined to be patched
  3. Inspect for symbolic links in agent directories
    Search for symbolic links within the agent installation and data directories. Use commands like 'find /opt/thousandeyes -type l -ls' and similar for /var/thousandeyes or the agent working directory. List all links in these paths
    Affected if Any symbolic link exists in the agent directories, especially if pointing to system files outside the agent's intended scope
  4. Verify permissions on agent directories
    Run 'ls -la' on the agent's root and subdirectories. Check that only the intended service account has write access and that no world-writable permissions exist on sensitive directories
    Affected if The agent directories have overly permissive write access or unexpected ownership
  5. Audit for recent file overwrites in system directories
    Review modification timestamps on critical system files using 'ls -lat /etc/passwd /etc/shadow /etc/sudoers' and compare to expected baselines. Check application logs for unexpected file write operations
    Affected if System files show unexpected modification timestamps or the logs indicate unauthorized file writes

A system is affected if ThousandEyes Enterprise Agent is installed and running, and suspicious symbolic links are present in agent directories or permissions have been modified to allow unauthorized file overwrites.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Cisco's patch when available; until then, restrict local CLI access to trusted low-privilege users and monitor for suspicious symbolic link creation in the agent's directories.

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,620
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-20161 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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