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ConnectApplication · Kerio

CVE-2011-1506

MEDIUM · 6.8 CVSS v2.0 Published 2011-03-22
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
77/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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
The STARTTLS implementation in Kerio Connect 7.1.4 build 2985 and MailServer 6.x 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. NOTE: some of these details are obtained from third party information.

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

The STARTTLS implementation in Kerio Connect 7.1.4 and MailServer 6.x fails to properly restrict I/O buffering during the TLS handshake transition. This allows a man-in-the-middle attacker to inject plaintext commands into what should be an encrypted SMTP session—these commands are processed after TLS negotiation completes, effectively bypassing the encryption layer.

MitigationUpgrade Kerio Connect and MailServer to versions that properly handle STARTTLS command buffering and ensure commands sent before TLS negotiation are not processed after the secure channel is established.

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
ConnectApplication
Affected:= 7.1.4
Kerio MailserverApplication
Affected:= 5.0= 5.1= 5.1.1= 5.6.3= 5.6.4= 5.6.5= 5.7.0= 5.7.1= 5.7.2= 5.7.3= 5.7.4= 5.7.5

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
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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Kerio product
    Check the installed application name - either Kerio Connect or Kerio MailServer. This can be found in the program's About section, installed programs list, or by querying the service name running on the system.
    Affected if The product is Kerio Connect version 7.1.4 or Kerio MailServer versions 5.0 through 5.7.5 (specifically 5.0, 5.1, 5.1.1, 5.6.3, 5.6.4, 5.6.5, 5.7.0, 5.7.1, 5.7.2, 5.7.3, 5.7.4, or 5.7.5)
  2. Confirm exact product version
    Locate the exact version number of the installed Kerio software. For Kerio Connect, check the About dialog or the administration interface. For Kerio MailServer, check the version in the admin panel or service information.
    Affected if The version matches exactly one of the affected versions listed in the CVE (7.1.4 for Connect, or any of 5.0, 5.1, 5.1.1, 5.6.3, 5.6.4, 5.6.5, 5.7.0, 5.7.1, 5.7.2, 5.7.3, 5.7.4, 5.7.5 for MailServer)
  3. Verify STARTTLS is enabled for SMTP
    Access the mail server administration console and check the SMTP server settings to determine if STARTTLS is enabled. Look for TLS/SSL or STARTTLS options in the SMTP configuration section.
    Affected if STARTTLS is enabled on the SMTP service - the vulnerability only applies when STARTTLS is in use, as the flaw involves improper I/O buffering during the TLS handshake transition
  4. Check SMTP service exposure
    Determine if the SMTP service accepting external connections is running the affected Kerio product. Verify port 25 (or configured SMTP port) is accessible and serviced by the vulnerable Kerio implementation.
    Affected if The affected Kerio product with STARTTLS enabled is accepting SMTP connections from untrusted networks, as the man-in-the-middle attack vector requires network proximity to the SMTP session

The environment is affected if running Kerio Connect 7.1.4 or Kerio MailServer versions 5.0-5.7.5 with STARTTLS enabled on an exposed SMTP service.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Kerio Connect and MailServer to versions that properly handle STARTTLS command buffering and ensure commands sent before TLS negotiation are not processed after the secure channel is established.

Fix this in Connect 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-2011-1506 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