CVE-2009-5138: Medium severity GNU GnuTLS vulnerability
GnuTLS before 2.7.6, when the GNUTLSVERIFYALLOWX509V1CACRT flag is not enabled, treats version 1 X.509 certificates as intermediate CAs, which allows remote attackers to bypass intended restrictions by leveraging a X.509 V1 certificate from a trusted CA to issue new certificates, a different vulnerability than CVE-2014-1959.
Other sources
While investigating GnuTLS issue CVE-2014-1959 (bug 1065092), it was discovered that older versions of GnuTLS were affected by the same problem, with a different root cause. When using default certificate verification settings, GnuTLS accepted version 1 X.509 certificates as intermediate CAs. An attacker able to obtain a V1 certificate from a CA trusted by application could generate certificates for other hosts or users that would be accepted by GnuTLS.
This issue affected GnuTLS versions before 2.7.6. Problem was reported in the following post:
http://thread.gmane.org/gmane.comp.encryption.gpg.gnutls.devel/3351/focus=3361
and fixed upstream via:
https://gitorious.org/gnutls/gnutls/commit/c8dcbedd1fdc312f5b1a70fcfbc1afe235d800cd
This did not affect applications that used GNUTLSVERIFYALLOWX509V1CACRT verification flag, which instructs GnuTLS to allow root CA certificates to be version 1 certificates. This was set by e.g. gnutls-cli client application in GnuTLS versions affected by this bug.
This issue affects gnutls packages in Red Hat Enterprise Linux 5. Versions used in Red Hat Enterprise Linux 6 or current Fedora versions are newer than 2.7.6 and are not affected.
— Red Hat
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2009-5138?
CVE-2009-5138 is classified as a moderate severity vulnerability due to its potential to allow unauthorized certificate issuance.
How do I fix CVE-2009-5138?
To fix CVE-2009-5138, update GnuTLS to version 2.7.6 or later, or enable the GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT flag.
What versions of GnuTLS are affected by CVE-2009-5138?
Versions of GnuTLS prior to 2.7.6 are affected by CVE-2009-5138.
Can CVE-2009-5138 be exploited remotely?
Yes, CVE-2009-5138 can be exploited remotely by attackers leveraging a X.509 V1 certificate from a trusted CA.
What is the impact of CVE-2009-5138 on certificate validation?
CVE-2009-5138 allows X.509 V1 certificates to be incorrectly treated as intermediate CAs, bypassing validation restrictions.