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Win CE schannel cert name out of buffer read

Project curl Security Advisory, December 21, 2016 - Permalink

VULNERABILITY

curl's TLS server certificate checks are flawed on Windows CE.

This vulnerability occurs in the verify certificate function when comparing a wildcard certificate name (as returned by the Windows API function CertGetNameString) to the hostname used to make the connection to the server.

The pattern matching logic exhibits an out of bounds read. If the wildcard certificate name field is longer than the connection host name, the wildcard comparison code will perform a buffer overread of the connection hostname heap based buffer. This issue could technically leak the contents of memory immediately preceding the connection hostname buffer, just a crash or at worst happen to match against another piece of data.

We are not aware of any exploit of this flaw.

INFO

This vulnerability only happens on libcurl built for Windows CE using the schannel TLS backend.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2016-9953 to this issue.

AFFECTED VERSIONS

This flaw exists in the following libcurl versions.

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

THE SOLUTION

In version 7.52.0, the certificate check is changed to instead use the libcurl certificate verifying function used for a few other TLS backends that doesn't contain these flaws.

A patch for CVE-2016-9953 is available. The patch is the identical one used for CVE-2016-9952.

RECOMMENDATIONS

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

A - Upgrade curl and libcurl to version 7.52.0

B - Apply the patch to your version and rebuild

C - Do not use the schannel backend on Windows CE

TIME LINE

It was first reported to the curl project on November 29 by Dan McNulty.

We contacted MITRE on December 13.

curl 7.52.0 was released on December 21 2016, coordinated with the publication of this advisory.

CREDITS

Reported and patched by Dan McNulty.