CVE-2009-3942
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 · uneditedMartin Lambers msmtp before 1.4.19, when OpenSSL is used, does not properly handle a '\0' character in a domain name in the (1) subject's Common Name or (2) Subject Alternative Name 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 confidencemsmtp before version 1.4.19 contains a vulnerability in X.509 certificate validation when using OpenSSL. The application fails to properly handle null characters ('\0') in the domain name within either the subject's Common Name (CN) or Subject Alternative Name (SAN) fields of an SSL certificate. This allows a malicious certificate issued by a legitimate Certificate Authority to be accepted as valid for a different domain, enabling man-in-the-middle attacks to spoof arbitrary SSL servers.
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<= 1.4.18= 0.2.5= 0.2.6= 0.3.0= 0.3.1= 0.4.0= 0.4.1= 0.4.2= 0.5.0= 0.5.1= 0.5.2= 0.5.3CVSS 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
- None
- Integrity
- Partial
- Availability
- Partial
AV:N/AC:L/Au:N/C:N/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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Verify msmtp is installedRun 'msmtp --version' or check your package manager for msmtp installationAffected if msmtp is not installed or the command fails
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Determine installed versionRun 'msmtp --version' to obtain the exact version numberAffected if version is 1.4.18 or lower, or matches any of these exact versions: 0.2.5, 0.2.6, 0.3.0, 0.3.1, 0.4.0, 0.4.1, 0.4.2, 0.5.0, 0.5.1, 0.5.2, 0.5.3
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Confirm SSL/TLS is enabledInspect msmtp configuration files (typically ~/.msmtprc or /etc/msmtprc) for 'tls on' or 'ssl on' directivesAffected if TLS or SSL is enabled in the configuration (the vulnerability only applies when encryption is used)
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Verify OpenSSL is the crypto backendCheck if msmtp was compiled against OpenSSL by reviewing build configuration or runtime output; the vulnerability exists specifically when OpenSSL is used for certificate validationAffected if OpenSSL is used as the SSL/TLS library (the flaw is in OpenSSL certificate validation handling)
You are affected if msmtp is installed with a vulnerable version AND SSL/TLS is enabled using the OpenSSL backend for certificate validation.
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 msmtp to version 1.4.19 or later to remediate this vulnerability. As a temporary workaround, verify certificate chains manually or disable SSL/TLS usage until the upgrade can be applied.
- Consultation1.0 h
- Implementation1.0 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-2009-3942 — 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-2009-3942 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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