CVE-2020-26161
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 · uneditedIn Octopus Deploy through 2020.4.2, an attacker could redirect users to an external site via a modified HTTP Host header.
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 confidenceOctopus Deploy through 2020.4.2 is vulnerable to HTTP Host header injection. The application uses the Host header value to construct redirect URLs without proper validation, allowing an attacker to modify the header and redirect users to external malicious sites.
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>= 2019.8.2, <= 2020.4.2CVSS 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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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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Identify Octopus Deploy versionLog into the Octopus Web UI and navigate to the System node > About page, or check the installation directory for a version file. Compare the version number to the affected range: 2019.8.2 through 2020.4.2 inclusive.Affected if The installed version falls within >= 2019.8.2 and <= 2020.4.2
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Confirm HTTP redirect functionality is in useReview the Octopus Deploy server configuration or HTTP response headers when making requests to the server. Observe if any HTTP 3xx redirects are returned to the client.Affected if The server issues HTTP redirects to clients
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Test for Host header reflection in redirectsSend a request to the Octopus server with a manipulated Host header (e.g., Host: attacker.com) and observe whether the redirect location header reflects this arbitrary Host value.Affected if Redirect responses contain the attacker-controlled Host header value rather than a trusted domain
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Inspect server configuration filesExamine the Octopus Deploy server configuration files (typically found in the installation directory) for any redirect rules or URL construction logic that uses the incoming Host header.Affected if Configuration shows redirect URLs being built using the incoming Host header without validation
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Check reverse proxy settingsIf Octopus is behind a reverse proxy or load balancer, inspect the proxy configuration to verify whether the Host header is being passed through and used for redirect construction.Affected if The proxy passes through the Host header and Octopus uses it for redirects
You are affected if your Octopus Deploy version is between 2019.8.2 and 2020.4.2 inclusive AND the server performs HTTP redirects that reflect the incoming Host header value.
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 allowlist-based validation for the HTTP Host header against trusted domains, and ensure all redirect operations use hardcoded trusted domain values rather than user-supplied Host header input.
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 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 $2,272.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-26161 — 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-2020-26161 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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- 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
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