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Octopus DeployApplication · Octopus

CVE-2021-26556

HIGH · 7.8 CVSS v3.1 Published 2021-10-07
Fix available
A fix is available. Upgrade to 2020.4.229 / 2020.5.256 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 Server 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 · moderate confidence

Octopus Server fails to set correct folder ACLs when installed to a custom folder location, creating a DLL side-loading vulnerability where an unprivileged attacker can place a malicious DLL in the Octopus folder and cause a privileged service to execute it, achieving privilege escalation.

MitigationReview and correct folder ACLs on the Octopus Server custom installation directory to ensure only privileged service accounts have write access; consider reinstalling with default paths or applying documented secure ACL configurations.

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
Octopus DeployApplication
Affected:>= 0.9, < 2020.4.229
Octopus ServerApplication
Affected:>= 2020.5.0, < 2020.5.256

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. Identify Octopus installation version
    Check the installed version of Octopus Server or Octopus Deploy. On Windows, this can be found in Programs and Features, or by checking the About section in the Octopus web interface. For command-line, check the server version via 'Octopus.Server.exe --version' if available in the installation directory.
    Affected if The installed version falls within 0.9 to 2020.4.229 for Octopus Deploy, or 2020.5.0 to 2020.5.256 for Octopus Server.
  2. Determine installation folder location
    Identify the folder where Octopus Server or Octopus Deploy is installed. Check the installation path shown in Programs and Features, or inspect the service configuration using 'sc qc OctopusDeploy' or 'sc qc OctopusServer' to find the binary path.
    Affected if The installation folder is a custom directory rather than the default installation path (typically C:\Program Files\Octopus Deploy\Octopus or similar default locations).
  3. Review folder permissions for write access
    Right-click the Octopus installation folder in Windows Explorer, select Properties, then the Security tab. Examine which users and groups have Write or Modify permissions to the folder. Alternatively, use 'icacls [installation_folder]' from an elevated command prompt to list all access control entries.
    Affected if Non-privileged users (such as standard user accounts or the Everyone group) have Write, Modify, or Full Control permissions to the Octopus installation folder.
  4. Inspect for modifiable DLL files
    Navigate to the Octopus installation folder and its subdirectories (particularly bin folders). Check for DLL files that are writable by non-privileged users. Use 'icacls [folder]\*.dll' to list DLL permissions.
    Affected if Any DLL files in the Octopus installation directory are writable by users who do not have privileged access to the system.

A user is affected if they run a vulnerable Octopus version (pre-2020.4.229 or pre-2020.5.256) installed to a custom folder where non-privileged accounts have write access to the installation directory or its DLL files.

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 2020.4.229 / 2020.5.256 or later
Fixed in 2020.4.2292020.5.256
Interim mitigation

Review and correct folder ACLs on the Octopus Server custom installation directory to ensure only privileged service accounts have write access; consider reinstalling with default paths or applying documented secure ACL configurations.

Recommended fix High confidence

2020.4.229 or later for Octopus Deploy; 2020.5.256 or later for Octopus Server 2020.5.x

  1. 1. Backup your current Octopus Deploy/Server installation and configuration
  2. 2. Identify your current version by checking the Octopus Server manager or running `Octopus.Server version`
  3. 3. If running Octopus Deploy (older branch), upgrade to version 2020.4.229 or later
  4. 4. If running Octopus Server 2020.5.x, upgrade to version 2020.5.256 or later
  5. 5. After upgrade, verify the custom folder ACLs are correctly set by reviewing folder permissions
  6. 6. Test that the Octopus service starts successfully and functions properly
Caveat Review release notes for any configuration or migration changes between your current version and the target upgrade version

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

Fix this in Octopus Deploy Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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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-2021-26556 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