The Heartbleed Bug
is a serious vulnerability in the popular OpenSSL cryptographic software
library. This weakness allows stealing the information protected, under normal
conditions, by the SSL/TLS encryption used to secure the Internet. SSL/TLS
provides communication security and privacy over the Internet for applications
such as web, email, instant messaging (IM) and some virtual private networks
The Heartbleed bug
allows anyone on the Internet to read the memory of the systems protected by
the vulnerable versions of the OpenSSL software. This compromises the secret
keys used to identify the service providers and to encrypt the traffic, the
names and passwords of the users and the actual content. This allows attackers
to eavesdrop on communications, steal data directly from the services and users
and to impersonate services and users.
What leaks in practice?
We have tested some
of our own services from attacker's perspective. We attacked ourselves from
outside, without leaving a trace. Without using any privileged information or
credentials we were able steal from ourselves the secret keys used for our
X.509 certificates, user names and passwords, instant messages, emails and
business critical documents and communication.
How to stop the leak?
As long as the
vulnerable version of OpenSSL is in use it can be abused. Fixed OpenSSL has been released and now it has to be
deployed. Operating system vendors and distribution, appliance vendors,
independent software vendors have to adopt the fix and notify their users.
Service providers and users have to install the fix as it becomes available for
the operating systems, networked appliances and software they use.
What is the CVE-2014-0160?
the official reference to this bug. CVE (Common Vulnerabilities and Exposures)
is the Standard for Information Security Vulnerability Names maintained by MITRE. Due
to co-incident discovery a duplicate CVE, CVE-2014-0346, which was assigned to
us, should not be used, since others independently went public with the
Why it is called the Heartbleed Bug?
Bug is in the
OpenSSL's implementation of the TLS/DTLS (transport layer security protocols)
heartbeat extension (RFC6520). When it is exploited it leads to the leak of
memory contents from the server to the client and from the client to the
What makes the Heartbleed Bug unique?
Bugs in single
software or library come and go and are fixed by new versions. However this bug
has left large amount of private keys and other secrets exposed to the
Internet. Considering the long exposure, ease of exploitation and attacks
leaving no trace this exposure should be taken seriously.
Is this a design flaw in SSL/TLS
No. This is
implementation problem, i.e. programming mistake in popular OpenSSL library
that provides cryptographic services such as SSL/TLS to the applications and
What is being leaked?
Encryption is used
to protect secrets that may harm your privacy or security if they leak. In
order to coordinate recovery from this bug we have classified the compromised
secrets to four categories: 1) primary key material, 2) secondary key material
and 3) protected content and 4) collateral.
What is leaked primary key material
and how to recover?
These are the crown
jewels, the encryption keys themselves. Leaked secret keys allows the attacker
to decrypt any past and future traffic to the protected services and to
impersonate the service at will. Any protection given by the encryption and the
signatures in the X.509 certificates can be bypassed. Recovery from this leak
requires patching the vulnerability, revocation of the compromised keys and
reissuing and redistributing new keys. Even doing all this will still leave any
traffic intercepted by the attacker in the past still vulnerable to decryption.
All this has to be done by the owners of the services.
What is leaked secondary key material
and how to recover?
These are for
example the user credentials (user names and passwords) used in the vulnerable
services. Recovery from this leaks requires owners of the service first to
restore trust to the service according to steps described above. After this
users can start changing their passwords and possible encryption keys according
to the instructions from the owners of the services that have been compromised.
All session keys and session cookies should be invalided and considered
What is leaked protected content and
how to recover?
This is the actual
content handled by the vulnerable services. It may be personal or financial
details, private communication such as emails or instant messages, documents or
anything seen worth protecting by encryption. Only owners of the services will
be able to estimate the likelihood what has been leaked and they should notify
their users accordingly. Most important thing is to restore trust to the
primary and secondary key material as described above. Only this enables safe
use of the compromised services in the future.
What is leaked collateral and how to
are other details that have been exposed to the attacker in the leaked memory
content. These may contain technical details such as memory addresses and
security measures such as canaries used to protect against overflow attacks.
These have only contemporary value and will lose their value to the attacker
when OpenSSL has been upgraded to a fixed version.
Recovery sounds laborious, is there a
After seeing what
we saw by "attacking" ourselves, with ease, we decided to take this
very seriously. We have gone laboriously through patching our own critical
services and are in progress of dealing with possible compromise of our primary
and secondary key material. All this just in case we were not first ones to
discover this and this could have been exploited in the wild already.
How revocation and reissuing of
certificates works in practice?
If you are a
service provider you have signed your certificates with a Certificate Authority
(CA). You need to check your CA how compromised keys can be revoked and new
certificate reissued for the new keys. Some CAs do this for free, some may take
Am I affected by the bug?
You are likely to
be affected either directly or indirectly. OpenSSL is the most popular open
source cryptographic library and TLS (transport layer security) implementation
used to encrypt traffic on the Internet. Your popular social site, your
company's site, commerce site, hobby site, site you install software from or
even sites run by your government might be using vulnerable OpenSSL. Many of
online services use TLS to both to identify themselves to you and to protect
your privacy and transactions. You might have networked appliances with logins
secured by this buggy implementation of the TLS. Furthermore you might have
client side software on your computer that could expose the data from your
computer if you connect to compromised services.
How widespread is this?
software using OpenSSL are the open source web servers like Apache and nginx.
The combined market share of just those two out of the active sites on the
Internet was over 66% according to Netcraft's April 2014 Web Server Survey.
Furthermore OpenSSL is used to protect for example email servers (SMTP, POP and
IMAP protocols), chat servers (XMPP protocol), virtual private networks (SSL
VPNs), network appliances and wide variety of client side software. Fortunately
many large consumer sites are saved by their conservative choice of SSL/TLS
termination equipment and software. Ironically smaller and more progressive
services or those who have upgraded to latest and best encryption will be
affected most. Furthermore OpenSSL is very popular in client software and
somewhat popular in networked appliances which have most inertia in getting
What versions of the OpenSSL are
Status of different
through 1.0.1f (inclusive) are vulnerable
OpenSSL 1.0.1g is
branch is NOT vulnerable
branch is NOT vulnerable
Bug was introduced
to OpenSSL in December 2011 and has been out in the wild since OpenSSL release
1.0.1 on 14th of March 2012. OpenSSL 1.0.1g released on 7th of April 2014 fixes
How common are the vulnerable OpenSSL
versions have been out there for over two years now and they have been rapidly
adopted by modern operating systems. A major contributing factor has been that
TLS versions 1.1 and 1.2 came available with the first vulnerable OpenSSL
version (1.0.1) and security community has been pushing the TLS 1.2 due to
earlier attacks against TLS (such as the BEAST).
How about operating systems?
system distributions that have shipped with potentially vulnerable OpenSSL
(stable), OpenSSL 1.0.1e-2+deb7u4
Ubuntu 12.04.4 LTS,
CentOS 6.5, OpenSSL
Fedora 18, OpenSSL
(OpenSSL 1.0.1c 10 May 2012) and 5.4 (OpenSSL 1.0.1c 10 May 2012)
FreeBSD 10.0 -
OpenSSL 1.0.1e 11 Feb 2013
distribution with versions that are not vulnerable:
(oldstable), OpenSSL 0.9.8o-4squeeze14
FreeBSD 8.4 -
OpenSSL 0.9.8y 5 Feb 2013
FreeBSD 9.2 -
OpenSSL 0.9.8y 5 Feb 2013
FreeBSD 10.0p1 -
OpenSSL 1.0.1g (At 8 Apr 18:27:46 2014 UTC)
FreeBSD Ports -
OpenSSL 1.0.1g (At 7 Apr 21:46:40 2014 UTC)
How can OpenSSL be fixed?
Even though the
actual code fix may appear trivial, OpenSSL team is the expert in fixing it
properly so latest fixed version 1.0.1g or newer should be used. If this is not
possible software developers can recompile OpenSSL with the handshake removed
from the code by compile time option -DOPENSSL_NO_HEARTBEATS.
Should heartbeat be removed to aid in
detection of vulnerable services?
Recovery from this
bug could benefit if the new version of the OpenSSL would both fix the bug and
disable heartbeat temporarily until some future version. It appears that
majority if not almost all TLS implementations that respond to the heartbeat
request today are vulnerable versions of OpenSSL. If only vulnerable versions
of OpenSSL would continue to respond to the heartbeat for next few months then
large scale coordinated response to reach owners of vulnerable services would
become more feasible.
Can I detect if someone has exploited
this against me?
this bug leaves no traces of anything abnormal happening to the logs.
Can IDS/IPS detect or block this
content of the heartbeat request is encrypted it has its own record type in the
protocol. This should allow intrusion detection and prevention systems
(IDS/IPS) to be trained to detect use of the heartbeat request. Due to
encryption differentiating between legitimate use and attack can not be based
on the content of the request, but the attack may be detected by comparing the
size of the request against the size of the reply. This seems to imply that
IDS/IPS can be programmed to detect the attack but not to block it unless
heartbeat requests are blocked altogether.
Has this been abused in the wild?
We don't know.
Security community should deploy TLS/DTLS honeypots that entrap attackers and
to alert about exploitation attempts.
Can attacker access only 64k of the
There is no total
of 64 kilobytes limitation to the attack, that limit applies only to a single
heartbeat. Attacker can either keep reconnecting or during an active TLS
connection keep requesting arbitrary number of 64 kilobyte chunks of memory
content until enough secrets are revealed.
Is this a MITM bug like Apple's goto
fail bug was?
No this doesn't
require a man in the middle attack (MITM). Attacker can directly contact the
vulnerable service or attack any user connecting to a malicious service.
However in addition to direct threat the theft of the key material allows man
in the middle attackers to impersonate compromised services.
Does TLS client certificate
authentication mitigate this?
request can be sent and is replied to during the handshake phase of the
protocol. This occurs prior to client certificate authentication.
Does OpenSSL's FIPS mode mitigate
No, OpenSSL Federal
Information Processing Standard (FIPS) mode has no effect on the vulnerable
Does Perfect Forward Secrecy (PFS)
Use of Perfect
Forward Secrecy (PFS), which is unfortunately rare but powerful, should protect
past communications from retrospective decryption. Please seehttps://twitter.com/ivanristic/status/453280081897467905 how
leaked tickets may affect this.
Can heartbeat extension be disabled
during the TLS handshake?
heartbeat extension code is activated regardless of the results of the
handshake phase negotiations. Only way to protect yourself is to upgrade to
fixed version of OpenSSL or to recompile OpenSSL with the handshake removed
from the code.
Who found the Heartbleed Bug?
This bug was
independently discovered by a team of security engineers (Riku, Antti and
Matti) atCodenomicon and
Neel Mehta of Google Security, who first reported it to the OpenSSL team.
Codenomicon team found heartbleed bug while improving the SafeGuard feature in
Codenomicon's Defensics security testing tools and reported this bug to the
NCSC-FI for vulnerability coordination and reporting to OpenSSL team.
What is the Defensics SafeGuard?
feature of the Codenomicon's Defensics security testtools automatically tests
the target system for weaknesses that compromise the integrity, privacy or
safety. The SafeGuard is systematic solution to expose failed cryptographic
certificate checks, privacy leaks or authentication bypass weaknesses that have
exposed the Internet users to man in the middle attacks and eavesdropping. In
addition to the Heartbleed bug the new Defensics TLS Safeguard feature can
detect for instance the exploitable security flaw in widely used GnuTLS open
source software implementing SSL/TLS functionality and the "goto fail;" bug
in Apple's TLS/SSL implementation that was patched in February 2014.
Who coordinates response to this
up the task of reaching out to the authors of OpenSSL, software, operating
system and appliance vendors, which were potentially affected. However, this
vulnerability was found and details released independently by others before
this work was completed. Vendors should be notifying their users and service
providers. Internet service providers should be notifying their end users where
and when potential action is required.
Is there a bright side to all this?
For those service
providers who are affected this is a good opportunity to upgrade security
strength of the secret keys used. A lot of software gets updates which
otherwise would have not been urgent. Although this is painful for the security
community, we can rest assured that infrastructure of the cyber criminals and
their secrets have been exposed as well.
Where to find more information?
This Q&A was
published as a follow-up to the OpenSSL advisory, since this vulnerability
became public on 7th of April 2014. The OpenSSL project has made a statement athttps://www.openssl.org/news/secadv_20140407.txt. NCSC-FI
published an advisory athttps://www.cert.fi/en/reports/2014/vulnerability788210.html.
Individual vendors of operating system distributions, affected owners of
Internet services, software packages and appliance vendors may issue their own
OpenSSL Security Advisory (published 7th of April 2014, ~17:30 UTC)
CloudFlare: Staying ahead of OpenSSL vulnerabilities (published 7th of April 2014, ~18:00 UTC)
heartbleed.com (published 7th of April 2014, ~19:00 UTC)