Vulnerability Note VU#732952
OpenSSL accepts unsolicited client certificate messages
OpenSSL accepts unsolicited client certificate messages. This could allow an attacker to exploit underlying vulnerabilities in client certificate handling.
OpenSSL implements the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols and includes a general-purpose cryptographic library. SSL and TLS are commonly used to provide authentication, encryption, integrity, and non-repudiation services to network applications such as HTTP, IMAP, POP3, LDAP, and others. Clients and servers exchange authentication information in X.509 certificates.
Both the (obsolete) SSL 3.0 standard and RFC 2246 (TLSv1) state that a client certificate message "...is only sent if the server requests a certificate." To minimize the opportunity for attacks, an SSL/TLS service should ignore unsolicited client certificate messages.
4. Due to an error in the SSL/TLS protocol handling, a server will parse a client certificate when one is not specifically requested. This by itself is not strictly speaking a vulnerability but it does mean that *all* SSL/TLS servers that use OpenSSL can be attacked using vulnerabilities 1, 2 and 3 even if they don't enable client authentication.
Vulnerability 1 refers to VU#935264. Vulnerability 2 refers to both VU#255484 and VU#380864. Vulnerability 3 refers to VU#686224.
Using specially crafted client certificate messages, a remote attacker can attempt to exploit underlying vulnerabilities in SSL/TLS ASN.1 parsing implementations. The impacts of these vulnerabilities (VU#935264, VU#255484, VU#380864, and VU#686224) are denial of service and possible execution of arbitrary code.
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Systems Affected (Learn More)
|Vendor||Status||Date Notified||Date Updated|
|OpenSSL||Affected||-||30 Sep 2003|
CVSS Metrics (Learn More)
Information used in this document came from OpenSSL and NISCC.
This document was written by Art Manion.
- CVE IDs: Unknown
- CERT Advisory: CA-2003-26
- Date Public: 04 Sep 2003
- Date First Published: 30 Sep 2003
- Date Last Updated: 01 Oct 2003
- Severity Metric: 2.53
- Document Revision: 15
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