CVE-2009-2666
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 · uneditedsocket.c in fetchmail before 6.3.11 does not properly handle a '\0' character in a domain name in the subject's Common Name (CN) field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority, a related issue to CVE-2009-2408.
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 confidenceThis is a null-byte injection vulnerability in fetchmail's SSL certificate validation. The socket.c component fails to properly handle a null character ('\0') embedded in the Common Name (CN) field of an X.509 certificate, allowing attackers to craft fraudulent certificates that bypass validation and enable man-in-the-middle attacks against SSL connections.
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<= 6.3.10= 4.5.1= 4.5.2= 4.5.3= 4.5.4= 4.5.5= 4.5.6= 4.5.7= 4.5.8= 4.6.0= 4.6.1= 4.6.2CVSS 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
- Authentication
- None
- Confidentiality
- Partial
- Integrity
- Partial
- Availability
- None
AV:N/AC:L/Au:N/C:P/I:P/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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Verify fetchmail is installedRun 'fetchmail --version' or check for the fetchmail package using your system package manager (e.g., dpkg -l | grep fetchmail, rpm -qa | grep fetchmail)Affected if fetchmail is installed and the version falls within the affected range (4.5.1 to 4.6.2, or 6.3.10 and below)
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Confirm installed version numberCompare the version output from the previous step against the affected versions: 4.5.1, 4.5.2, 4.5.3, 4.5.4, 4.5.5, 4.5.6, 4.5.7, 4.5.8, 4.6.0, 4.6.1, 4.6.2, or any version 6.3.10 or lowerAffected if The installed version matches one of the listed affected versions
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Check if SSL/TLS is configuredInspect your fetchmail configuration file (typically ~/.fetchmailrc or /etc/fetchmailrc) for 'ssl', 'sslcertck', or 'sslfingerprint' directives in any pop3, imap, or etrn poll entriesAffected if SSL or TLS is enabled in the fetchmail configuration for any mail server connection
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Inspect SSL certificate validation settingsLook for any 'sslcertck' (certificate checking) or 'sslfingerprint' settings in the fetchmailrc file to determine if certificate validation is in useAffected if SSL is configured but certificate validation settings are absent or weak, making the null-byte injection bypass possible
You are affected if fetchmail is installed with a version between 4.5.1-4.6.2 or 6.3.10 and below, and SSL/TLS is enabled for mail retrieval, as this creates the condition where the null-byte certificate validation bypass can be exploited.
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 fetchmail to version 6.3.11 or later which contains the patched certificate validation code. Alternatively, verify SSL certificates manually or use additional certificate pinning as a workaround until upgrade is possible.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2009-2666 — 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-2009-2666 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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