CVE-2021-36806
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 · uneditedA reflected XSS vulnerability allows an open redirect when the victim clicks a malicious link to an error page on Sophos Email Appliance older than version 4.5.3.4.
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 confidenceA reflected cross-site scripting (XSS) vulnerability combined with an open redirect flaw exists in the error page handling of Sophos Email Appliance versions prior to 4.5.3.4. Attackers can craft malicious URLs that when clicked by victims redirect them to attacker-controlled sites or execute arbitrary JavaScript in the context of the vulnerable domain.
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< 4.5.3.4CVSS 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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Confirm Sophos Email Appliance is deployedIdentify whether Sophos Email Appliance exists in your environment by checking your asset inventory, network services, or appliance management console for the product name 'Sophos Email Appliance'Affected if The product is not present in your environment, then you are not affected
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Determine the installed version of Sophos Email ApplianceAccess the appliance management interface or command-line console and retrieve the current firmware/software version number. This is typically found in System > About, Dashboard, or via CLI command 'version' or 'show system-info'Affected if The version cannot be determined or the appliance is not accessible for version check, treat as potentially vulnerable until verified
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Compare installed version against affected rangeTake the retrieved version number and compare it to the affected range: any version prior to 4.5.3.4 is vulnerable. Check if your version is < 4.5.3.4Affected if Installed version is 4.5.3.4 or later, then you are not affected by this CVE; if version is lower than 4.5.3.4 or cannot be confirmed, you may be affected
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Assess exposure of the web interfaceDetermine if the appliance's web-based management interface or user-facing email portal is accessible from network locations where attackers could send malicious links. Check firewall rules, VPN requirements, and authentication policiesAffected if The error page handling is reachable by unauthenticated or low-privilege users without additional filtering, exploitation is possible
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Test for XSS or open redirect in error pagesIf permitted by your security policy, safely test by accessing the appliance with a crafted URL such as https://<appliance-host>/error?msg=<script>alert(1)</script> or a redirect parameter, and observe if the payload is reflected unescaped or if redirection occursAffected if The payload is reflected in the response without encoding or the browser redirects to an arbitrary URL, the vulnerability is confirmed present
You are affected if Sophos Email Appliance is running and the version is lower than 4.5.3.4, with the web interface accessible to potential attackers who could send malicious URLs.
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.
dbcve · scoped4.5.3.4
Upgrade Sophos Email Appliance to version 4.5.3.4 or later to remediate this vulnerability. Until upgrade is possible, consider filtering or blocking malicious links via email security gateways.
4.5.3.4 or later
- 1. Identify the current version of Sophos Email Appliance currently installed
- 2. Upgrade Sophos Email Appliance to version 4.5.3.4 or later
- 3. After upgrade, verify the version number is 4.5.3.4 or higher
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-36806 — 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-2021-36806 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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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.
- 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