{"id":1628,"date":"2014-04-12T08:19:37","date_gmt":"2014-04-12T15:19:37","guid":{"rendered":"http:\/\/blog.mozilla.org\/security\/?p=1628"},"modified":"2016-09-30T02:52:23","modified_gmt":"2016-09-30T09:52:23","slug":"testing-for-heartbleed-vulnerability-without-exploiting-the-server","status":"publish","type":"post","link":"https:\/\/blog.mozilla.org\/security\/2014\/04\/12\/testing-for-heartbleed-vulnerability-without-exploiting-the-server\/","title":{"rendered":"Testing for Heartbleed vulnerability without exploiting the server."},"content":{"rendered":"

Heartbleed is a serious vulnerability in OpenSSL that was disclosed on Tuesday, April 8th, and impacted any sites or services using OpenSSL 1.01 – 1.01.f and 1.0.2-beta1. Due to the nature of the bug, the only obvious way to test a server for the bug was an invasive attempt to retrieve memory–and this could lead to the compromise of sensitive data and\/or potentially crash the service.<\/p>\n

I developed a new test case that neither accesses sensitive data nor impacts service performance, and am posting the details here to help organizations conduct safe testing for Heartbleed vulnerabilities. While there is a higher chance of a false positive, this test should be safe to use against critical services.<\/p>\n

The test works by observing a specification implementation error in vulnerable versions of OpenSSL: they respond to larger than allowed HeartbeatMessages.<\/p>\n

Details:<\/b><\/em>
\nOpenSSL was patched by commit 731f431<\/a>. This patch addressed 2 implementation issues with the Heartbeat extension<\/a>:<\/p>\n

    \n
  1. HeartbeatRequest message specifying an erroneous payload length<\/li>\n
  2. Total HeartbeatMessage length exceeding 2^14 (16,384 bytes)<\/li>\n<\/ol>\n

    Newer versions of OpenSSL silently discard messages which fall into the above categories. It is possible to detect older versions of OpenSSL by constructing a HeartbeatMessage and not sending padding bytes. This results in the below evaluating true:<\/p>\n

    \/* Read type and payload length first *\/\r\nif (1 + 2 + 16 > s->s3->rrec.length)\r\n  return 0; \/* silently discard *\/\r\n<\/pre>\n
    Vulnerable versions of OpenSSL will respond to the request. However no server memory will be read because the client sent payload_length bytes.<\/p>\n
    False positives may occur when all the following conditions are met (but it is unlikely):<\/p>\n
      \n
    1. The service uses a library other than OpenSSL<\/li>\n
    2. The library supports the Heartbeat extension<\/li>\n
    3. The service has Heartbeat enabled<\/li>\n
    4. The library performs a fixed length padding check similar to OpenSSL<\/li>\n<\/ol>\n
      False negatives may occur when all the following conditions are met, and can be minimized by repeating the test:<\/p>\n
        \n
      1. The service uses a vulnerable version of OpenSSL<\/li>\n
      2. The Heartbeat request isn\u2019t received by the testing client<\/li>\n<\/ol>\n
        I have modified the Metasploit openssl_heartbleed module to support the \u2018check\u2019 option.<\/p>\n
        You can download the updated module at
        \n        https:\/\/github.com\/dchan\/metasploit-framework\/blob\/master\/modules\/auxiliary\/scanner\/ssl\/openssl_heartbleed.rb<\/a><\/p>\n
        We hope you can use this to test your servers and make sure any vulnerable ones get fixed!<\/p>\n
        David Chan
        \nMozilla Security Engineer<\/p>\n","protected":false},"excerpt":{"rendered":"
        Heartbleed is a serious vulnerability in OpenSSL that was disclosed on Tuesday, April 8th, and impacted any sites or services using OpenSSL 1.01 – 1.01.f and 1.0.2-beta1. Due to the … Read more<\/a><\/p>\n","protected":false},"author":1438,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[69,45499,610,73],"tags":[45493,45494,265,45495],"coauthors":[45547],"yoast_head":"\nTesting for Heartbleed vulnerability without exploiting the server. - Mozilla Security Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blog.mozilla.org\/security\/2014\/04\/12\/testing-for-heartbleed-vulnerability-without-exploiting-the-server\/\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"mozilla\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/blog.mozilla.org\/security\/2014\/04\/12\/testing-for-heartbleed-vulnerability-without-exploiting-the-server\/\",\"url\":\"https:\/\/blog.mozilla.org\/security\/2014\/04\/12\/testing-for-heartbleed-vulnerability-without-exploiting-the-server\/\",\"name\":\"Testing for Heartbleed vulnerability without exploiting the server. - 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