oss-security - [SECURITY ADVISORY] curl: CVE-2023-27538: SSH connection too eager reuse still

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Message-ID: <s3sr40p2-p54p-803q-4313-30opr383p732@unkk.fr>
Date: Mon, 20 Mar 2023 08:26:21 +0100 (CET)
From: Daniel Stenberg <daniel@...x.se>
To: curl security announcements -- curl users <curl-users@...ts.haxx.se>, 
    curl-announce@...ts.haxx.se, libcurl hacking <curl-library@...ts.haxx.se>, 
    oss-security@...ts.openwall.com
Subject: [SECURITY ADVISORY] curl: CVE-2023-27538: SSH connection too eager
 reuse still

CVE-2023-27538: SSH connection too eager reuse still
====================================================

Project curl Security Advisory, March 20th 2023 -
[Permalink](https://curl.se/docs/CVE-2023-27538.html)

VULNERABILITY
-------------

libcurl would reuse a previously created connection even when an SSH related
option had been changed that should have prohibited reuse.

libcurl keeps previously used connections in a connection pool for subsequent
transfers to reuse if one of them matches the setup. However, two SSH settings
were left out from the configuration match checks, making them match too
easily.

We are not aware of any exploit of this flaw.

INFO
----

These are the options that were not considered in the check, so curl would
reuse a connection even if the subsequent transfer would have changed one or
more of these options.

- `CURLOPT_SSH_PUBLIC_KEYFILE`
- `CURLOPT_SSH_PRIVATE_KEYFILE`

This flaw was initially introduced in curl 7.16.1.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2023-27538 to this issue.

This vulnerability is partially identical to
[CVE-2022-27782](https://curl.se/docs/CVE-2022-27782.html) since the fix for
that previous issue was bad and did not actually correct the problem for these
SSH options.

CWE-305: Authentication Bypass by Primary Weakness

The previos flaw CVE-2022-27782 was set to severity Medium, but since this is
a partial of that and affects only two options that rarely will change with
the expectation that the user will be different, this time we set it severity
Low.

Severity: Low

AFFECTED VERSIONS
-----------------

- Affected versions: curl 7.16.1 to and including 7.88.1
- Not affected versions: curl < 7.16.1 and curl >= 8.0.0

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

THE SOLUTION
------------

The fix for [CVE-2023-27538](https://github.com/curl/curl/commit/af369db4d3833272b8ed)

RECOMMENDATIONS
--------------

  A - Upgrade curl to version 8.0.0

  B - Apply the patch to your local version

  C - Avoid SCP and SFTP transfers

TIMELINE
--------

This issue was reported to the curl project on March 9 2023. We contacted
distros@...nwall on March 13, 2023.

curl 8.0.0 was released on March 20 2023, coordinated with the publication of
this advisory.

CREDITS
-------

- Reported-by: Harry Sintonen
- Patched-by: Daniel Stenberg

Thanks a lot!

-- 

  / daniel.haxx.se
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