curl / Docs / curl CVEs / IDNA 2003 makes curl use wrong host


IDNA 2003 makes curl use wrong host

Project curl Security Advisory, November 2, 2016 - Permalink


When curl is built with libidn to handle International Domain Names (IDNA), it translates them to puny code for DNS resolving using the IDNA 2003 standard, while IDNA 2008 is the modern and up-to-date IDNA standard.

This misalignment causes problems with for example domains using the German ß character (known as the Unicode Character LATIN SMALL LETTER SHARP S) which is used at times in the .de TLD and is translated differently in the two IDNA standards, leading to users potentially and unknowingly issuing network transfer requests to the wrong host.

For example, straß is translated into using IDNA 2003 but is translated into using IDNA 2008. Needless to say, those hostnames could very well resolve to different addresses and be two completely independent servers. IDNA 2008 is mandatory for .de domains.

curl is not alone with this problem, as there is currently a big flux in the world of network user-agents about which IDNA version to support and use.

This name problem exists for DNS-using protocols in curl, but only when built to use libidn.


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2016-8625 to this issue.

CWE-838: Inappropriate Encoding for Output Context

Severity: High


This flaw exists in the following curl versions.

libcurl is used by many applications, but not always advertised as such!


In version 7.51.0, the parser function is fixed.


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

A - Upgrade curl and libcurl to version 7.51.0

B - Apply the patch to your version and rebuild


It was first reported to the curl project on October 11.

We contacted distros@openwall on October 19.

curl 7.51.0 was released on November 2 2016, coordinated with the publication of this advisory.


Thanks a lot!