curl / Docs / Security Problems / use-after-free in handle close

use-after-free in handle close

Project curl Security Advisory, October 31st 2018 - Permalink


libcurl contains a heap use-after-free flaw in code related to closing an easy handle.

When closing and cleaning up an "easy" handle in the Curl_close() function, the library code first frees a struct (without nulling the pointer) and might then subsequently erroneously write to a struct field within that already freed struct.

We are not aware of any exploit of this flaw.


This bug was introduced in commit b46cfbc068, February 2018.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2018-16840 to this issue.

CWE-416: Use After Free

Severity: 2.3 (Low)


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


A patch for CVE-2018-16840 is available.


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

A - Upgrade curl to version 7.62.0

B - Apply the patch to your version and rebuild


It was reported to the curl project on October 14, 2018. We contacted distros@openwall on October 22.

curl 7.62.0 was released on October 31 2018, coordinated with the publication of this advisory.


Reported by Brian Carpenter, Geeknik Labs. Patch by Daniel Stenberg.

Thanks a lot!