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double-free in krb5 code

Project curl Security Advisory, November 2, 2016 - Permalink

VULNERABILITY

In curl's implementation of the Kerberos authentication mechanism, the function read_data() in security.c is used to fill the necessary krb5 structures. When reading one of the length fields from the socket, it fails to ensure that the length parameter passed to realloc() is not set to 0.

This would lead to realloc() getting called with a zero size and when doing so realloc() returns NULL and frees the memory - in contrary to normal realloc() fails where it only returns NULL - causing libcurl to free the memory again in the error path.

This flaw could be triggered by a malicious or just otherwise ill-behaving server.

We are not aware of any exploit of this flaw.

INFO

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2016-8619 to this issue.

AFFECTED VERSIONS

This flaw exists in the following curl versions

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

THE SOLUTION

In version 7.51.0, the function reading data will consider reading a zero size to be an error and bail out.

A patch for CVE-2016-8619 is available.

RECOMMENDATIONS

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

C - Do not use KRB5

TIME LINE

It was first reported to the curl project on September 23 by Cure53.

We contacted distros@openwall on October 19.

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

CREDITS

This vulnerability was found during a Secure Open Source audit performed by Cure53.