--write-out out of buffer read
Project curl Security Advisory, April 3, 2017 - Permalink
VULNERABILITY
There were two bugs in curl's parser for the command line option --write-out
(or -w for short) that would skip the end of string zero byte if the string
ended in a % (percent) or \ (backslash), and it would read beyond that
buffer in the heap memory and it could then potentially output pieces of that
memory to the terminal or the target file etc.
The curl security team did not report this as a security vulnerability due to the minimal risk: the memory this would output comes from the process the user itself invokes and that runs with the same privileges as the user. We could not come up with a likely scenario where this could leak other users' data or memory contents.
An external party registered this as a CVE with
mitre.org and
we feel a responsibility to clarify what this flaw is about. The CVE-2017-7407
issue is specifically only about the % part of this flaw.
This flaw only exists in the command line tool.
We are not aware of any exploit of this flaw.
INFO
The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2017-7407 to this issue.
CWE-126: Buffer Over-read
AFFECTED VERSIONS
curl has supported this option since version 6.5 (released March 13, 2000).
This flaw exists in the following curl versions.
THE SOLUTION
In version 7.54.0, the end of the buffer is properly acknowledged and we have added tests that verify this functionality.
The curl project has (as of this writing) not yet released a version with this problem fixed. It is however already fixed in curl's git repository, commits 1890d59905414ab and 8e65877870c1. The fix is also available as a stand-alone patch.
RECOMMENDATIONS
We suggest you take one of the following actions immediately, in order of preference:
A - Upgrade curl and libcurl to version 7.54.0
B - Apply the patch to your version and rebuild
C - Do not use the --write-out feature with unchecked input
TIME LINE
It was first reported to the curl project on March 10. The Mitre CVE registration was brought to our attention on April 4, 2017. The first commit to fix this was made public on March 11.
curl 7.54.0 is to be released on April 19 2017
CREDITS
Reported to the curl project by Brian Carpenter