oss-security - [SECURITY ADVISORY] curl: TELNET stack contents disclosure again

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Message-ID: <nycvar.QRO.7.76.2107210915010.25537@fvyyl>
Date: Wed, 21 Jul 2021 09:15:24 +0200 (CEST)
From: Daniel Stenberg <daniel@...x.se>
To: curl security announcements -- curl users <curl-users@...l.haxx.se>, 
    curl-announce@...l.haxx.se, libcurl hacking <curl-library@...l.haxx.se>, 
    oss-security@...ts.openwall.com
Subject: [SECURITY ADVISORY] curl: TELNET stack contents disclosure again

TELNET stack contents disclosure again
======================================

Project curl Security Advisory, July 21st 2021 -
[Permalink](https://curl.se/docs/CVE-2021-22925.html)

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

curl supports the `-t` command line option, known as `CURLOPT_TELNETOPTIONS`
in libcurl. This rarely used option is used to send variable=content pairs to
TELNET servers.

Due to flaw in the option parser for sending `NEW_ENV` variables, libcurl
could be made to pass on uninitialized data from a stack based buffer to the
server. Therefore potentially revealing sensitive internal information to the
server using a clear-text network protocol.

This could happen because curl did not call and use sscanf() correctly when
parsing the string provided by the application.

The previous curl security vulnerability
[CVE-2021-22898](https://curl.se/docs/CVE-2021-22898.html) is almost identical
to this one but the fix was insufficient so this security vulnerability
remained.

We are not aware of any exploit of this flaw.

INFO
----

This flaw has existed in curl since commit
[a1d6ad2610](https://github.com/curl/curl/commit/a1d6ad2610) in libcurl 7.7,
released on March 22, 2001. There was a previous attempt to fix this issue in
curl 7.77.0 but it was not done proper.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2021-22925 to this issue.

CWE-457: Use of Uninitialized Variable

Severity: Medium

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

- Affected versions: curl 7.7 to and including 7.77.0
- Not affected versions: curl < 7.7 and curl >= 7.78.0

Also note that libcurl is used by many applications, and not always advertised
as such.

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

Use sscanf() properly and only use properly filled-in buffers.

A [fix for CVE-2021-22925](https://github.com/curl/curl/commit/894f6ec730597eb243618d33cc84d71add8d6a8a)

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

  A - Upgrade curl to version 7.78.0

  B - Apply the patch to your local version

  C - Avoid using `CURLOPT_TELNETOPTIONS`

TIMELINE
--------

This issue was reported to the curl project on June 11, 2021.

This advisory was posted on July 21, 2021.

CREDITS
-------

This issue was reported and patched by Red Hat Product Security.

Thanks a lot!

-- 

  / daniel.haxx.se
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