curl / Docs / Security / NTLM buffer overflow via integer overflow

NTLM buffer overflow via integer overflow

Project curl Security Advisory, November 29th 2017 - Permalink

VULNERABILITY

libcurl contains a buffer overrun flaw in the NTLM authentication code.

The internal function Curl_ntlm_core_mk_ntlmv2_hash sums up the lengths of the user name + password (= SUM) and multiplies the sum by two (= SIZE) to figure out how large storage to allocate from the heap.

The SUM value is subsequently used to iterate over the input and generate output into the storage buffer. On systems with a 32 bit size_t, the math to calculate SIZE triggers an integer overflow when the combined lengths of the user name and password is larger than 2GB (2^31 bytes). This integer overflow usually causes a very small buffer to actually get allocated instead of the intended very huge one, making the use of that buffer end up in a buffer overrun.

We are not aware of any exploit of this flaw.

INFO

This bug was introduced in commit 86724581b6c02d160b5, January 2014.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2017-8816 to this issue.

AFFECTED VERSIONS

This is only an issue on 32 bit systems. It also requires the user and password fields to use more than 2GB of memory combined, which in itself should be rare.

curl is used by many applications, but not always advertised as such.

THE SOLUTION

In libcurl version 7.57.0, the integer overflow is avoided.

A patch for CVE-2017-8816 is available.

RECOMMENDATIONS

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

A - Upgrade curl to version 7.57.0

B - Apply the patch to your version and rebuild

C - Put length restrictions on the user name and passwords you can pass to libcurl

TIME LINE

It was reported to the curl project on November 6, 2017. We contacted distros@openwall on November 21.

curl 7.57.10 was released on November 29 2017, coordinated with the publication of this advisory.

CREDITS

Reported by Alex Nichols. Patch by Daniel Stenberg.

Thanks a lot!