CVE-2011-2165
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 · uneditedThe STARTTLS implementation in WatchGuard XCS 9.0 and 9.1 does not properly restrict I/O buffering, which allows man-in-the-middle attackers to insert commands into encrypted SMTP sessions by sending a cleartext command that is processed after TLS is in place, related to a "plaintext command injection" attack, a similar issue to CVE-2011-0411.
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 confidenceThe STARTTLS implementation in WatchGuard XCS 9.0 and 9.1 improperly restricts I/O buffering, allowing man-in-the-middle attackers to inject plaintext commands into encrypted SMTP sessions after TLS negotiation completes. This plaintext command injection occurs because the server processes commands from its buffer even after TLS encryption is established, enabling the attacker to bypass the encryption layer.
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= 9.0= 9.1CVSS 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
- M
- Authentication
- None
- Confidentiality
- Partial
- Integrity
- Partial
- Availability
- Partial
AV:N/AC:M/Au:N/C:P/I:P/A:P
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 WatchGuard XCS deploymentIdentify if WatchGuard XCS mail security appliance or software is running in your environment. Check system inventory, appliance management console, or running services for 'WatchGuard' or 'XCS' product signatures.Affected if WatchGuard XCS is not present in the environment, this CVE does not apply.
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Check XCS versionAccess the WatchGuard XCS admin console or command line interface and run: 'version' or 'show system info' to retrieve the installed software version.Affected if The installed version is exactly 9.0 or 9.1. Versions other than 9.0 and 9.1 are not affected by this specific CVE.
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Verify STARTTLS is enabledAccess the XCS mail gateway configuration for SMTP settings. Check if STARTTLS support is enabled in the SMTP server configuration. This can be done via the admin web interface under Mail > SMTP > Security, or via CLI command 'smtp show' or 'tls show'.Affected if STARTTLS is disabled in the SMTP configuration. The vulnerability only affects systems where STARTTLS is enabled, as the flaw occurs during TLS negotiation.
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Inspect SMTP traffic handlingReview SMTP proxy or gateway logs for STARTTLS negotiation patterns. Use packet capture on SMTP traffic port 25 to observe whether TLS upgrade is being performed. Check XCS SMTP proxy policies for TLS enforcement settings.Affected if STARTTLS negotiation completes without proper buffer flush. The vulnerability exists when commands remain in the I/O buffer after TLS upgrade, allowing injection.
You are affected if WatchGuard XCS version 9.0 or 9.1 is installed AND STARTTLS is enabled in the SMTP configuration, allowing plaintext command injection after TLS negotiation.
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 dataUpgrade WatchGuard XCS to a patched version that properly flushes or restricts I/O buffers upon STARTTLS negotiation, or disable STARTTLS if no patch is available.
- Consultation2.0 h
- Implementation3.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,040.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2011-2165 — 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-2011-2165 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
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