curl / Docs / Security Problems / HTTP Proxy deny use-after-free

CVE-2022-43552: HTTP Proxy deny use-after-free

Project curl Security Advisory, December 21 2022 - Permalink


curl can be asked to tunnel virtually all protocols it supports through an HTTP proxy. HTTP proxies can (and often do) deny such tunnel operations using an appropriate HTTP error response code.

When getting denied to tunnel the specific protocols SMB or TELNET, curl would use a heap-allocated struct after it had been freed, in its transfer shutdown code path.

We are not aware of any exploit of this flaw.


This flaw was introduced for TELNET in commit b7eeb6e67fca68 in September 7, 2006. The SMB part was introduced in 2014 with commit aec2e865f06669.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2022-43552 to this issue.

CWE-416: Use After Free

Severity: Low


libcurl is used by many applications, but not always advertised as such!


A fix for CVE-2022-43552


A - Upgrade curl to version 7.87.0

B - Apply the patch to your local version

C - Avoid using SMB and TELNET or disable HTTP proxy use


This issue was reported to the curl project on November 7, 2022. We contacted distros@openwall on December 12, 2022.

curl 7.87.0 was released on December 21 2022, coordinated with the publication of this advisory.


Thanks a lot!