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Heartbleed

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This is an old revision of this page, as edited by Lopifalko (talk | contribs) at 11:55, 15 April 2014 (→‎Software applications: Added various vulnerable applications culled from http://security.stackexchange.com/questions/55119/does-the-heartbleed-vulnerability-affect-clients-as-severely (sorry, no refs)). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Logo representing Heartbleed. Security company Codenomicon gave Heartbleed both a name and a logo, contributing to public awareness of the issue.[1][2]

Heartbleed is a security bug in the open-source OpenSSL cryptography library, widely used to implement the Internet's Transport Layer Security (TLS) protocol. This vulnerability is due to a missing bounds check in the handling of the Transport Layer Security (TLS) heartbeat extension.[3] A fixed version of OpenSSL was released on April 7, 2014, at the same time as Heartbleed was publicly disclosed. At that time, some 17 percent (around half a million) of the Internet's secure web servers certified by trusted authorities were believed to be vulnerable to the attack, allowing theft of the servers' private keys and users' session cookies and passwords.[4][5][6][7][8] The Electronic Frontier Foundation,[9] Ars Technica,[10] and Bruce Schneier[11] all deemed the Heartbleed bug "catastrophic". Forbes cybersecurity columnist Joseph Steinberg wrote, "Some might argue that [Heartbleed] is the worst vulnerability found (at least in terms of its potential impact) since commercial traffic began to flow on the Internet."[12]

A United States Cabinet spokesman recommended that "People should take advice on changing passwords from the websites they use... Most websites have corrected the bug and are best placed to advise what action, if any, people need to take."[13] On the day of disclosure, the Tor Project advised anyone seeking "strong anonymity or privacy on the Internet" to "stay away from the Internet entirely for the next few days while things settle."[14]

Heartbleed is registered in the Common Vulnerabilities and Exposures system as CVE-2014-0160.[15] The federal Canadian Cyber Incident Response Centre issued a security bulletin advising system administrators about the bug.[16]

History

Appearance

The Heartbeat Extension for the Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) protocols is a proposed standard specified by RFC 6520, published in February 2012. It provides a way to test and keep alive secure communication links without the need to renegotiate the connection each time.

In 2011, Dr. Robin Seggelmann, then a Ph.D. student at the University of Duisburg-Essen, implemented the Heartbeat Extension for OpenSSL. Following Seggelmann's request to put the result of his work into OpenSSL,[17][18][19] his change was reviewed by Dr. Stephen N. Henson, one of OpenSSL's four core developers. Henson apparently failed to notice a bug in Seggelmann's implementation, and introduced the resulting vulnerability, Heartbleed, into OpenSSL's source code repository on December 31, 2011. Heartbeat support was enabled by default, causing affected versions to be affected by default. The vulnerable code has been adopted to widespread use with the release of OpenSSL version 1.0.1 on March 14, 2012.[20][21][22]

Discovery

According to Mark J. Cox of OpenSSL, Neel Mehta of Google's security team reported Heartbleed on April 1, 2014.[23] The bug entailed a severe memory handling error in the implementation of the Transport Layer Security Heartbeat Extension.[24][25] This defect could be used to reveal up to 64 kilobytes of the application's memory with every heartbeat.[25]

The bug was named by an engineer at the firm Codenomicon, a Finnish cybersecurity company, which also created the bleeding heart logo, and launched the domain Heartbleed.com to explain the bug to the public.[26] According to Codenomicon, Neel Mehta first reported the bug to OpenSSL, but both Google and Codenomicon discovered it independently.[20] Codenomicon reports April 3 as their date of discovery of the bug and as their date of notification of NCSC-FI (formerly known as CERT-FI) for vulnerability coordination.[20][27] Mehta also congratulated Codenomicon, without going into detail.[28]

The Sydney Morning Herald published a timeline of the discovery on April 15.[29]

Resolution

On March 21, 2014 Bodo Moeller and Adam Langley of Google wrote a patch that fixed the bug. The date of the patch is known from Red Hat's issue tracker.[30] The next chronological date available from the public evidence is the claim by performance and security company CloudFlare that they fixed the flaw on their systems on March 31, 2014.[31]

On April 10, "Cisco Systems and Juniper Networks, two of the biggest creators of Internet equipment, announced on Thursday that their products had been affected by the Heartbleed bug. Routers, firewalls and switches ... have all likely been affected by the bug, leaving your personal information at risk of being stolen by hackers."[32]

Exploitation

The Canada Revenue Agency reported the theft of Social Insurance Numbers belonging to 900 taxpayers, and stated that they were accessed through an exploit of the bug during a 6-hour period on April 8.[33] When the attack was discovered, the agency shut down its web site and extended the taxpayer filing deadline from April 30 to May 5.[34] The agency said it will provide anyone affected with credit protection services at no cost.

On April 12, at least two independent researchers were able to steal private keys using this attack from an experimental server intentionally set up for that purpose by CloudFlare.[35][36]

Claims of possible knowledge and exploitation prior to disclosure

Many major web sites patched or disabled the bug within days of its announcement,[37] but it is unclear whether potential attackers were aware of it earlier and to what extent it was exploited. Based on examinations of audit logs by researchers, it has been reported that some attackers may have exploited the flaw for at least five months before discovery and announcement.[38][39] Errata Security has partially rejected this hypothesis.[40]

According to Bloomberg News, two unnamed insider sources informed it that the United States National Security Agency were aware of the flaw since shortly after its introduction, but chose to keep it secret, instead of reporting it, in order to exploit it for their own purposes.[41][42][43] The NSA has denied this claim.[44]

Behavior

Depiction of Heartbleed

The RFC 6520 Heartbeat Extension tests TLS/DTLS secure communication links by allowing a computer at one end of a connection to send a “Heartbeat Request” message, consisting of a payload, typically a text string, along with the payload’s length as a 16-bit integer. The receiving computer then must send the exact same payload back to the sender.

The affected versions of OpenSSL allocate a memory buffer for the message to be returned based on the length field in the requesting message, without regard to the size of actual payload in that message. Because of this failure to do proper bounds checking, the message returned consists of the requested payload followed by whatever else happened to be in the allocated memory buffer. The problem was compounded by OpenSSL's decision to write its own version of the C dynamic memory allocation (malloc and free) routines. As a result, the oversized memory buffer returned to the requestor was likely to contain data from memory blocks that had been previously requested and freed by OpenSSL. Such memory blocks may contain sensitive data sent by users or even the private keys used by OpenSSL. In addition, by using its own memory management routines OpenSSL bypassed mitigation measures in some operating systems that might have detected or neutralized the bug.[45]

The heartbleed bug is exploited by sending a malformed heartbeat request with a small payload and large length field to the server in order to elicit the server's response permitting attackers to read up to 64 kilobytes of server memory that was likely to have been used previously by SSL.[46] Attackers in this way could receive sensitive data, compromising the security of the server and its users. Vulnerable data include the server's private master key,[20][22] which would enable attackers to decrypt current or stored traffic via passive eavesdropping (if perfect forward secrecy is not used by the server and client), or active man-in-the-middle attacks if perfect forward secrecy is used. The attacker cannot control which data are returned, as OpenSSL typically responds with the chunks of memory it has most recently discarded.

The bug might also reveal unencrypted parts of users' requests and responses, including any form post data in users' requests, session cookies and passwords, which might allow attackers to hijack the identity of another user of the service.[47]

Impact

By attacking a service that uses a vulnerable version of OpenSSL, a remote, unauthenticated attacker may be able to retrieve sensitive information, such as secret keys. By leveraging this information, an attacker may be able to decrypt, spoof, or perform man-in-the-middle attacks on network traffic that would otherwise be protected by OpenSSL.[48]

Affected OpenSSL installations

The affected versions of OpenSSL are OpenSSL 1.0.1 through 1.0.1f (inclusive). Later versions (1.0.1g and ulterior[49]) and previous versions (1.0.0 branch and older) are not vulnerable.[50] Installations of the affected versions are vulnerable unless OpenSSL was compiled with OPENSSL_NO_HEARTBEATS.[25]

Vulnerable program and function

The vulnerable program source files are t1_lib.c and dl_both.c and the vulnerable functions are tls1_process_heartbeat() and dtls1_process_heartbeat().[51]

Patch

The bug is classified as a buffer over-read,[15] a situation where software allows more data to be read than should be allowed.[52] The problem can be fixed by ignoring Heartbeat Request messages that ask for more data than their payload needs.

Version 1.0.1g of OpenSSL adds some bounds checks to prevent the buffer over-read. For example, the test

if (1 + 2 + payload + 16 > s->s3->rrec.length) return 0; /* silently discard per RFC 6520 sec. 4 */

has been added in front of the line

pl = p;

A complete list of changes is available at git.openssl.org.[53]

Although patching software (the OpenSSL library and any statically linked binaries) fixes the bug, running software will continue to use its in-memory OpenSSL code with the bug until each application is shut down and restarted, so that the patched code can be loaded. Further, in order to regain privacy and secrecy, all private or secret data must be replaced, since it is not possible to know if they were compromised while the vulnerable code was in use:[54]

  • all possibly compromised private key-public key pairs must be regenerated,
  • all certificates linked to those possibly compromised key pairs need to be revoked and replaced, and
  • all passwords on the possibly compromised servers need to be changed.

Vulnerability testing services

Several services were made available to test whether the Heartbleed bug was present on a given site, including:

  • Arbor Network's Pravail Security Analytics
  • Heartbleed testing tool by a European IT security company[55]
  • Heartbleed Scanner by Italian cryptologist Filippo Valsorda[56]
  • Heartbleed Vulnerability Test by Cyberoam [57]
  • Critical Watch Free Online Heartbleed Tester[58]
  • Metasploit Heartbleed scanner module[59]
  • Heartbleed Server Scanner by Rehmann[60]
  • Lookout Mobile Security Heartbleed Detector, an app for Android devices that determines the OpenSSL version of the device and indicates whether the vulnerable heartbeat is enabled[61]
  • Heartbleed checker hosted by LastPass[62]
  • Online network range scanner for Heartbleed vulnerability by Pentest-Tools.com [63]
  • Official offline scanner in Python from Redhat "https://access.redhat.com/labs/heartbleed/heartbleed-poc.py". {{cite web}}: External link in |title= (help)
  • Qualys SSL Labs' SSL Server Test which not only looks for the Heartbleed bug, but can also find other SSL/TLS implementation errors.
  • Browser extensions, such as Chromebleed and FoxBleed.

Other security tools have added support for finding this bug. For example, Sourcefire has released Snort rules to detect Heartbleed attack traffic and possible Heartbleed response traffic.[64] Tenable Network Security wrote a plugin for its Nessus vulnerability scanner that can scan for this fault.[65]

Affected services

Websites and web services

An analysis posted on GitHub of the top 1000 most visited websites on April 8, 2014 revealed vulnerabilities in sites including Yahoo!, Imgur, Stack Overflow, Slate, and DuckDuckGo.[66][67] The following sites have services affected or made announcements recommending that users update passwords in response to the bug:

The Canadian federal government temporarily shut online services of the Canada Revenue Agency (CRA) and several government departments over Heartbleed bug security concerns.[92][93]

Platform maintainers like the Wikimedia Foundation advised their users to change passwords.[89]

The Tor Project recommended that Tor relay operators and hidden service operators revoke and generate fresh keys after patching OpenSSL, but noted that Tor relays use two sets of keys and that Tor's multi-hop design minimizes the impact of exploiting a single relay.[14]

Software applications

  • IPCop 2.1.4 was released on April 8, 2014 with a fix for "the OpenSSL library everybody is talking about".[94]
  • LastPass Password Manager was not vulnerable, due to its use of forward secrecy, but it recommended users change passwords that LastPass stored for vulnerable websites.[95]
  • LibreOffice 4.2.3 was released on April 10, 2014 with a fix for CVE-2014-0160[96]
  • LogMeIn claimed to have "updated many products and parts of our services that rely on OpenSSL".[97]
  • MariaDB 5.5.36 is reputed to be vulnerable
  • wget 1.15 leaks memory of earlier connections and own state
  • curl 7.36.0 is reputed to be vulnerable
  • git 1.9.1 tested clone / push, leaks not much
  • nginx 1.4.7 in proxy mode, leaks memory of previous requests
  • links 2.8 leaks contents of previous visits
  • All KDE applications using KIO (Dolphin, Konqueror)
  • Exim mailserver
  • OwnCloud

In addition, the Common Vulnerabilities and Exposures database, associated with the US Department of Homeland Security, advises that the following companies have had their software/products affected by Heartbleed:

  • McAfee and in particular some versions of software providing anti-viral coverage for Microsoft Exchange, software firewalls, and McAfee Email and Web Gateways [98]
  • Ubuntu operating system [99]
  • VMware series of Horizon products, emulators and cloud computing suites [100]

Root causes and possible lessons

Theo de Raadt, founder and leader of the OpenBSD and OpenSSH projects, has criticized the OpenSSL developers for writing their own memory management routines and thereby circumventing OpenBSD C standard library exploit countermeasures, saying "OpenSSL is not developed by a responsible team." [101][45]

The author of the change which introduced Heartbleed, Robin Seggelmann,[102] stated that he "missed validating a variable containing a length" and denied any intention to submit a flawed implementation.[17] Following Heartbleed's disclosure, Seggelmann has stated that OpenSSL is not reviewed by enough people.[103]

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