ares_create_query single byte out of buffer write

Project c-ares Security Advisory, September 29, 2016 - Permalink


When a string is passed in to ares_create_query or ares_mkquery and uses an escaped trailing dot, like "hello\.", c-ares calculates the string length wrong and subsequently writes outside of the allocated buffer with one byte. The wrongly written byte is the least significant byte of the 'dnsclass' argument; most commonly 1.

Proof of concept code have showed how this can be exploited in a real-world system, but we are not aware of any exploits having actually happened in the wild.


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2016-5180 to this issue.


This flaw exists in the following c-ares versions.


In version 1.12.0, the function has been corrected and a test case have been added to verify.

A patch for CVE-2016-5180 is available.


We suggest you take one of the following actions immediately, in order of preference:

A - Upgrade c-ares to version 1.12.0

B - Apply the patch to your version and rebuild

C - Make really sure you don't pass in strings to either of these functions that use escaped trailing dots.


It was reported to the c-ares project on September 22 by Gzob Qq.

c-ares 1.12.0 was released on September 29 2016, coordinated with the publication of this advisory.


Thanks to Gzob Qq for the report and to Mattias Nissler for code reviews of the patch.