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[SECURITY AVISORY] curl: FTP shutdown response buffer overflow

From: Daniel Stenberg <>
Date: Wed, 16 May 2018 08:25:56 +0200 (CEST)

FTP shutdown response buffer overflow

Project curl Security Advisory, May 16th 2018 -


curl might overflow a heap based memory buffer when closing down an FTP
connection with very long server command replies.

When doing FTP transfers, curl keeps a spare "closure handle" around
internally that will be used when an FTP connection gets shut down since the
original curl easy handle is then already removed.

FTP server response data that gets cached from the original transfer might
then be larger than the default buffer size (16 KB) allocated in the "closure
handle", which can lead to a buffer overwrite. The contents and size of that
overwrite is controllable by the server.

This situation was detected by an assert() in the code, but that was of course
only preventing bad stuff in debug builds. This bug is very unlikely to
trigger with non-malicious servers.

We are not aware of any exploit of this flaw.


This bug was introduced in April 2017 in [this
commit]( when we
introduced the use of increased buffer sizes for FTP.
The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2018-1000300 to this issue.
CWE-122: Heap-based Buffer Overflow
- Affected versions: curl 7.54.1 to and including curl 7.59.0
- Not affected versions: curl < 7.54.1 and curl >= 7.60.0
libcurl is used by many applications, but not always advertised as such.
In curl version 7.60.0, curl will return an error if this situation happens.
A [patch for CVE-2018-1000300]( is
We suggest you take one of the following actions immediately, in order of
  A - Upgrade curl to version 7.60.0
  B - Apply the patch to your version and rebuild
  C - Avoing using FTP
It was reported to the curl project on March 22, 2018
We contacted distros_at_openwall on May 7, 2018.
curl 7.60.0 was released on May 16 2018, coordinated with the publication of
this advisory.
Detected by Dario Weisser. Patch by Daniel Stenberg.
Thanks a lot!
Received on 2018-05-16