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Windows OpenSSL engine code injection

Project curl Security Advisory, June 24th 2019 - Permalink


A non-privileged user or program can put code and a config file in a known non-privileged path (under C:/usr/local/) that will make curl automatically run the code (as an OpenSSL "engine") on invocation. If that curl is invoked by a privileged user it can do anything it wants.

This flaw exists in the official curl-for-windows binaries built and hosted by the curl project (all versions up to and including 7.65.1_1). It does not exist in the curl executable shipped by Microsoft, bundled with Windows 10. It possibly exists in other curl builds for Windows too that uses OpenSSL.

The curl project has provided official curl executable builds for Windows since late August 2018.

There exists proof of concept exploits of this flaw.


This bug sneaked in partly due to insecure default build options in OpenSSL when built cross-compiled and partly due to a misleading commit message in the curl commit that made it possible to disable this feature.

This bug does not exist in the curl or libcurl source code but in the scripts for the Windows build.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2019-5443 to this issue.

CWE-94: Code Injection

Severity: High



Replace your downloaded curl version on Windows with the updated download package from the curl site.

The build fix for curl-for-win correcting this flaw is in this commit. It completely disables curl's ability to load an OpenSSL config when invoked.


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

A - Upgrade to a fixed curl executable

B - Remove curl executable downloaded from and instead use the one shipped by Microsoft in Windows 10


The issue was reported to the curl project on June 12, 2019. The fix was done, verified and communicated with the reporter on June 12, 2019.

While planning the release schedule of this advisory and coordinating with other affected projects, we discovered that this exact flaw had already been published and discussed in public before we were informed about it. A few other OpenSSL-using projects on Windows also had already fixed their builds for this exact problem. Realizing this, we switched gears and decided to publish as soon as possible to minimize user impact.

curl 7.65.1_2 for Windows was uploaded and made available on June 21 2019 - the older, vulnerable builds, were removed from the site at the same time.

This advisory was posted on June 24th 2019.


OpenSSL patch by Viktor Szakats.

Thanks a lot!