CVE-2011-1473: Medium severity openssl vulnerability
DISPUTED OpenSSL before 0.9.8l, and 0.9.8m through 1.x, does not properly restrict client-initiated renegotiation within the SSL and TLS protocols, which might make it easier for remote attackers to cause a denial of service (CPU consumption) by performing many renegotiations within a single connection, a different vulnerability than CVE-2011-5094. NOTE: it can also be argued that it is the responsibility of server deployments, not a security library, to prevent or limit renegotiation when it is inappropriate within a specific environment.
Other sources
It was reported [1] that a flaw exists in how openSSL handles SSL renegotiation. Because of the processing power required to handle an SSL/TLS handshake, with renegotiation enabled, a user can send multiple handshakes per second due to the renegotiation request being permitted. This could allow a malicious user to send multiple renegotiation requests and exhaust server resources.
Note that this is not the only way to cause a denial of service on an SSL-enabled service; there are many other ways to accomplish the same thing, this just makes it easier.
What makes this bug even more confusing is that this report is recent, with a 2011 CVE, however the recommended fix in the report is to upgrade to OpenSSL 0.9.8l, which is what disabled renegotiation, however it was subsequently re-enabled when OpenSSL added support for RFC5746 in OpenSSL 0.9.8m (which the reporter seems to imply isn't sufficient). I'm not sure where the CVE assignment came from; on MITRE's site is is reserved yet and I have not seen this discussed anywhere else but in a Nessus scan report [2].
As an aside, and to reference something we may need to look at, there seems to be some concern with Apache and how it works with SSL renegotiation disabled [3], so we will need to look into cases where disabling SSL renegotiation may impact expected behaviour of currently released products.
[1] http://orchilles.com/2011/03/ssl-renegotiation-dos.html [2] https://discussions.nessus.org/message/10629 [3] http://old.nabble.com/TLS-renegotiation-disabling-%3A-modssl-and-OpenSSL--0.9.8l-td26285568.html
— Red Hat
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2011-1473?
CVE-2011-1473 has a designation that indicates a denial of service vulnerability potentially affecting server performance.
How do I fix CVE-2011-1473?
To mitigate CVE-2011-1473, upgrade OpenSSL to a version that is newer than 0.9.8l.
What systems are affected by CVE-2011-1473?
CVE-2011-1473 affects multiple versions of OpenSSL including 0.9.8k and earlier versions.
Can CVE-2011-1473 be exploited remotely?
Yes, CVE-2011-1473 can be exploited remotely, allowing attackers to initiate numerous renegotiations.
What are the consequences of an exploit of CVE-2011-1473?
Exploiting CVE-2011-1473 may lead to denial of service through excessive CPU consumption due to continuous renegotiations.