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Date: Wed, 26 Oct 2022 08:26:48 +0200 (CEST)
From: Daniel Stenberg <>
To: curl security announcements -- curl users <>,, libcurl hacking <>,
Subject: [SECURITY ADVISORY] CVE-2022-42916: HSTS bypass via IDN (curl)

CVE-2022-42916: HSTS bypass via IDN

Project curl Security Advisory, October 26 2022 -


curl's HSTS check could be bypassed to trick it to keep using HTTP.

Using its HSTS support, curl can be instructed to use HTTPS directly instead
of using an insecure clear-text HTTP step even when HTTP is provided in the
URL. This mechanism could be bypassed if the host name in the given URL uses
IDN characters that get replaced to ASCII counterparts as part of the IDN
conversion. Like using the character UTF-8 U+3002 (IDEOGRAPHIC FULL STOP)
instead of the common ASCII full stop (U+002E) `.`.

Like this: `http://curl。se。`

We are not aware of any exploit of this flaw.


This flaw was introduced in [commit
7385610d0c7](, which was
shipped enabled by default from [commit
d71ff2b9db566b3f]( in
curl 7.77.0.

This issue is similar to the previous [CVE-2022-30115](

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2022-42916 to this issue.

CWE-319: Cleartext Transmission of Sensitive Information

Severity: Medium


- Affected versions: curl 7.77.0 to and including 7.85.0
- Not affected versions: curl < 7.77.0 and curl >= 7.86.0

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


A [fix for CVE-2022-42916](


  A - Upgrade curl to version 7.86.0

  B - Apply the patch to your local version

  C - Stick to always using `HTTPS://` in URLs


This issue was reported to the curl project on October 11, 2022. We contacted
distros@...nwall on October 18, 2022.

libcurl 7.86.0 was released on October 26 2022, coordinated with the
publication of this advisory.


- Reported-by: Hiroki Kurosawa
- Patched-by: Daniel Stenberg

Thanks a lot!


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