Cloudflare, Inc. is a U.S. organization that gives a content delivery network, Internet security services, and dispersed domain name server services, sitting between the customer and the Cloudflare client’s hosting provider, going about as a reverse proxy for sites.

Cloudflare was leaking a wide range of sensitive information, including authentication cookies and login accreditation, the flaw was named Cloudbleed.

Tavis Ormandy from Google’s Project Zero reached Cloudflare to report the security issue with their edge servers.

The leaked information included “private messages from real dating websites, full messages from a famous chat service, online password manager information, outlines from adult video sites, hotel appointments,” as per Tavis Ormandy.


Their edge servers were running past the finish of a buffer and returning memory that contained private data, such as, HTTP cookies, authentication tokens, HTTP POST bodies, and other sensitive information. Furthermore, some of that information had been stored via search indexes.

Period of impact

This bug was introduced in the HTML Parser component on September 22, 2016. Cloudflare resolved the issue on February 18, 2017, after the incident reported by Google security researcher.

The best time of effect was from February 13 and February 18 with around 1 in each 3,300,000 HTTP requests through Cloudflare possibly bringing about memory spillage (that is around 0.00003% of request).

Web crawlers, such as, Google (GOOG, – 0.56%), Yahoo (YHOO, – 0.13%), and Microsoft’s (MSFT, – 0.31%) Bing had accidentally put away released information as a feature of their web crawlers’ caches and CloudFlare group attempting to clean those data.

Root cause of the bug

The root cause of the bug was that achieving the finish of a buffer was checked utilizing the correspondence operator and a pointer was able to step the finish of the buffer. This is known as a buffer overrun.

/* generated code */
if ( ++p == pe )
 goto _test_eof;

The underlying bug occurs because of a pointer error.

Had the check been done using >= instead of == jumping over the buffer end would have been caught,” said Cumming.

Bug Fix Timeline – Cloudflare

  • 2017-02-18 0011 Tweet from Tavis Ormandy asking for Cloudflare contact information 2017-02-18 0032 Cloudflare receives details of bug from Google
  • 2017-02-18 0040 Cross-functional team assembles in San Francisco
  • 2017-02-18 0119 Email Obfuscation disabled worldwide
  • 2017-02-18 0122 London team joins
  • 2017-02-18 0424 Automatic HTTPS Rewrites disabled worldwide
  • 2017-02-18 0722 Patch implementing kill switch for cf-HTML parser deployed worldwide.
  • 2017-02-20 2159 SAFE_CHAR fix deployed globally
  • 2017-02-21 1803 Automatic HTTPS Rewrites, Server-Side Excludes, and Email Obfuscation re-enabled worldwide.

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