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TentacleApplication · Octopus

CVE-2021-26557

HIGH · 7.8 CVSS v3.1 Published 2021-10-07
Fix available
A fix is available. Upgrade to 6.0.489 or later.
See remediation →
81/100
Remediation priority · High
No privileges

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
When Octopus Tentacle is installed using a custom folder location, folder ACLs are not set correctly and could lead to an unprivileged user using DLL side-loading to gain privileged access.

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 confidence

Octopus Tentacle installer fails to set correct Access Control Lists (ACLs) on custom folder locations during installation. This permission misconfiguration allows unprivileged users to perform DLL side-loading attacks, where malicious DLLs can be placed in the improperly secured folder and executed with elevated privileges when the Tentacle service runs.

MitigationEnsure Tentacle is installed using default folder locations, or manually verify and correct folder permissions after installation to restrict write access to privileged service accounts only.

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
TentacleApplication
Affected:>= 3.15.4, < 6.0.489

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
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

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. Verify Octopus Tentacle is installed
    Check for the presence of Octopus Tentacle installation by looking for the installation directory, typically in Program Files\Octopus Tentacle, or check Windows Services for 'Octopus Tentacle' service using 'services.msc'
    Affected if Tentacle is installed and the service exists
  2. Determine installed Tentacle version
    Open Programs and Features (appwiz.cpl), find Octopus Tentacle in the list, and note the version column. Alternatively, check the file version of Tentacle.exe in the installation folder
    Affected if Version is >= 3.15.4 AND < 6.0.489
  3. Identify custom installation folder locations
    Review the installation configuration or check registry key HKLM\SOFTWARE\Octopus\Tentacle for custom paths configured during setup, particularly custom application and deployment folders
    Affected if Non-default folder locations were used during installation (folders other than the Program Files default)
  4. Inspect ACLs on custom folders
    Right-click the custom folder location in Windows Explorer, go to Properties > Security tab, and review the permissions. Verify which users and groups have Write or Full Control permissions
    Affected if Unprivileged users or groups (such as Users, Authenticated Users, or Everyone) have Write or Modify permissions to the custom folder
  5. Check for unauthorized DLL files in custom folders
    Navigate to the custom folder location and examine the contents for any DLL files that were not part of the original installation. Use 'dir /a' command to list all files including hidden ones
    Affected if Unexpected or suspicious DLL files exist in the custom folder that could be used for DLL side-loading

You are affected if Tentacle version is between 3.15.4 and 6.0.489 inclusive, custom non-default folders were used during installation, and those folders grant write access to unprivileged users.

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.

dbcve · scoped
Upgrade available Upgrade to 6.0.489 or later
Fixed in 6.0.489
Interim mitigation

Ensure Tentacle is installed using default folder locations, or manually verify and correct folder permissions after installation to restrict write access to privileged service accounts only.

Recommended fix High confidence

Upgrade to Tentacle version 6.0.489 or later (the latest stable 6.x release)

  1. 1. Identify the current Octopus Tentacle version by running 'Tentacle --version' or checking the installed programs list
  2. 2. If running version >= 3.15.4 and < 6.0.489, plan for upgrade to version 6.0.489 or later
  3. 3. Download the latest Tentacle installer from the official Octopus Downloads page (downloads.octopus.com)
  4. 4. Back up your Tentacle configuration and any custom scripts before upgrading
  5. 5. Stop the Octopus Tentacle service before upgrading
  6. 6. Run the installer and follow the upgrade prompts
  7. 7. Verify the service starts successfully after upgrade
  8. 8. Confirm the new version is installed by running 'Tentacle --version'
Caveat Review Octopus 6.0 release notes for any breaking changes from earlier versions; may require coordination with Octopus Server version compatibility

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Tentacle Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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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-2021-26557 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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data