curl / Docs / Security Problems / FTP shutdown response buffer overflow

FTP shutdown response buffer overflow

Project curl Security Advisory, May 16th 2018 - Permalink


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

Severity: High


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 available.


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

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@openwall on May 7, 2018.

curl 7.60.0 was released on May 16 2018, coordinated with the publication of this advisory.


Thanks a lot!