libcurl3 crashes when reusing handle with proxy NTLM authentication

[Patrick Steinhardt]

The package libcurl3-7.35.0 on Ubuntu Trusty crashes when reusing a curl handle and turning on proxy NTLM authentication. The libgit2 project is repeatedly hitting this issue on the new Travis CI container infrastructure, which they have recently updated to make use of Ubuntu Trusty.

This issue stems from the backported fix to CVE-2016-0755 (NTLM: Fix ConnectionExists to compare Proxy credentials), which introduces a null-pointer exception when one of the proxy credentials is `NULL`. The issue has already been fixed upstream in commit fa5fa65a309f352284e58f52183d586886eb17ea, which should be backported to fix the segfault. See the attached patch from Isaac Boukris.

Please consider including this patch to fix the fix for CVE-2016-0755.

[Edward Thomson (ethomson)]

I was pleased to see that there was a new trusty-updates package for curl that fixes a number of out-of-bounds reads!

And I was immediately disappointed that it didn't fix _this_ set of out-of-bounds reads.

Alas.