[Pkg-openssl-devel] Bug#672456: CVE-2011-1473: SSL/TLS DoS via repeated SSL session renegotiations

[Henri Salo]

Package: openssl
Version: 0.9.8o-4squeeze12
Severity: important
Tags: security

https://bugzilla.redhat.com/show_bug.cgi?id=707065
"""
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-mod_ssl-and-OpenSSL--0.9.8l-td26285568.html
"""

-- System Information:
Debian Release: 6.0.4
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.32-5-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to en_US.UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages openssl depends on:
ii  libc6                  2.11.3-3          Embedded GNU C Library: Shared lib
ii  libssl0.9.8            0.9.8o-4squeeze12 SSL shared libraries
ii  zlib1g                 1:1.2.3.4.dfsg-3  compression library - runtime

openssl recommends no packages.

Versions of packages openssl suggests:
ii  ca-certificates    20090814+nmu3squeeze1 Common CA certificates

-- no debconf information