{"id":11702,"date":"2015-07-15T14:41:57","date_gmt":"2015-07-15T18:41:57","guid":{"rendered":"http:\/\/mjtsai.com\/blog\/?p=11702"},"modified":"2015-07-15T14:43:40","modified_gmt":"2015-07-15T18:43:40","slug":"font-parsing-vulnerabilities","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2015\/07\/15\/font-parsing-vulnerabilities\/","title":{"rendered":"Font Parsing Vulnerabilities"},"content":{"rendered":"<p><a href=\"http:\/\/yahoo-security.tumblr.com\/post\/123981052855\/font-parsing-vulnerabilities\">John Villamil<\/a>:<\/p>\n<blockquote cite=\"http:\/\/yahoo-security.tumblr.com\/post\/123981052855\/font-parsing-vulnerabilities\">\n<p>During my research into various OS X frameworks I chose to focus on OS X font parsing and spent a week fuzzing and reversing native libraries. This research resulted in six CVEs, five of which are shared between OS X and iOS.<\/p>\n<p>Client side font parsing is often a good target because the file formats are varied and complicated. For example, TrueType comes with its own turing complete instruction set which you can learn more about <a href=\"https:\/\/developer.apple.com\/fonts\/TrueType-Reference-Manual\/\">here<\/a>. OTF and the less popular PostScript file formats are complex and also supported.<\/p>\n<p>Many of these flaws are the result of using untrusted length values extracted directly from the file without validation. In one example CoreText, a low level font layout framework, the ArabicLookups::AddLookup function (shown below) reads a length value from the memory mapped font file, using it to increment a pointer out of bounds. The pointer is held in the rdi register which is later dereferenced in the ResolveLookup function.<\/p>\n<\/blockquote>","protected":false},"excerpt":{"rendered":"<p>John Villamil: During my research into various OS X frameworks I chose to focus on OS X font parsing and spent a week fuzzing and reversing native libraries. This research resulted in six CVEs, five of which are shared between OS X and iOS. Client side font parsing is often a good target because the [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"apple_news_api_created_at":"","apple_news_api_id":"","apple_news_api_modified_at":"","apple_news_api_revision":"","apple_news_api_share_url":"","apple_news_coverimage":0,"apple_news_coverimage_caption":"","apple_news_is_hidden":false,"apple_news_is_paid":false,"apple_news_is_preview":false,"apple_news_is_sponsored":false,"apple_news_maturity_rating":"","apple_news_metadata":"\"\"","apple_news_pullquote":"","apple_news_pullquote_position":"","apple_news_slug":"","apple_news_sections":"\"\"","apple_news_suppress_video_url":false,"apple_news_use_image_component":false,"footnotes":""},"categories":[2],"tags":[131,394,133,31,904,30,903,48],"class_list":["post-11702","post","type-post","status-publish","format-standard","hentry","category-technology","tag-bug","tag-coretext","tag-font","tag-ios","tag-ios-8","tag-mac","tag-mac-os-x-10-10-yosemite","tag-security"],"apple_news_notices":[],"_links":{"self":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/11702","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/comments?post=11702"}],"version-history":[{"count":1,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/11702\/revisions"}],"predecessor-version":[{"id":11703,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/11702\/revisions\/11703"}],"wp:attachment":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/media?parent=11702"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/categories?post=11702"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/tags?post=11702"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}