CVE-2009-3639
MEDIUMEPSS 92th pctlDescription
The mod_tls module in ProFTPD before 1.3.2b, and 1.3.3 before 1.3.3rc2, when the dNSNameRequired TLS option is enabled, does not properly handle a '\0' character in a domain name in the Subject Alternative Name field of an X.509 client certificate, which allows remote attackers to bypass intended client-hostname restrictions via a crafted certificate issued by a legitimate Certification Authority, a related issue to CVE-2009-2408.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v2 Vector
No CVSS vector data available.
Exploit Intelligence
High risk: more likely to be exploited than 92% of all known CVEs.
References
Related Vulnerabilities
Other CWE-310 (Cryptographic Issues) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2014-3566 | Low | 3.4 | 100% | - | Fix |
| CVE-2015-4000 | Low | 3.7 | 100% | - | Fix |
| CVE-2015-0204 | Medium | 4.3 | 99% | - | Fix |
| CVE-2016-2107 | Medium | 5.9 | 89% | - | Fix |
| CVE-2016-0800 | Medium | 5.9 | 82% | - | Fix |
| CVE-2014-8684 | Critical | 9.8 | 72% | - | - |
Common questions
How do I fix CVE-2009-3639?
Upgrade proftpd-dfsg on debian 11 to 1.3.2a-2 or later.
Is CVE-2009-3639 being actively exploited?
Not that we know of. CVE-2009-3639 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 5.7% is the estimated probability that it will be exploited in the next 30 days. That is higher than 92% of all scored CVEs.
How severe is CVE-2009-3639?
CVE-2009-3639 has a CVSS v2 base score of 5.8, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2009-3639 affect?
Published advisories record a fix for proftpd-dfsg (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-23.