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glob parser write/read out of bounds

Project curl Security Advisory, November 2, 2016 - Permalink

VULNERABILITY

The curl tool's "globbing" feature allows a user to specify a numerical range through which curl will iterate. It is typically specified as [1-5], specifying the first and the last numbers in the range. Or with [a-z], using letters.

  1. The curl code for parsing the second unsigned number did not check for a leading minus character, which allowed a user to specify [1--1] with no complaints and have the latter -1 number get turned into the largest unsigned long value the system can handle. This would ultimately cause curl to write outside the dedicated malloced buffer after no less than 100,000 iterations, since it would have room for 5 digits but not 6.

  2. When the range is specified with letters, and the ending letter is left out [L-], the code would still advance its read pointer 5 bytes even if the string was just 4 bytes and end up reading outside the given buffer.

This flaw exists only in the curl tool, not in the libcurl library.

We are not aware of any exploit of this flaw.

INFO

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2016-8620 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-2016-8620 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 - Switch off globbing or make sure you have all ranges in use verified!

TIME LINE

It was first reported to the curl project on October 2 by Luật Nguyễn.

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

Thanks to Luật Nguyễn.