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Date: Wed, 27 Apr 2022 08:40:18 +0200 (CEST)
From: Daniel Stenberg <>
To: curl security announcements -- curl users <>,, libcurl hacking <>,
Subject: [SECURITY ADVISORY] curl OAUTH2 bearer bypass in connection re-use

OAUTH2 bearer bypass in connection re-use

Project curl Security Advisory, April 27th 2022 -


libcurl might reuse OAUTH2-authenticated connections without properly making
sure that the connection was authenticated with the same credentials as set
for this transfer. This affects SASL-enabled protocols: SMPTP(S), IMAP(S),
POP3(S) and LDAP(S) (openldap only).

libcurl maintains a pool of live connections after a transfer has completed
(sometimes called the connection cache). This pool of connections is then gone
through when a new transfer is requested and if there is a live connection
available that can be reused, it is preferred instead of creating a new one.

Due to this security vulnerability, a connection that is successfully created
and authenticated with a user name + OAUTH2 bearer could subsequently be
erroneously reused even for user + [other OAUTH2 bearer], even though that
might not even be a valid bearer. This could lead to an authentication bypass,
either by mistake or by a malicious actor.

We are not aware of any exploit of this flaw.


This flaw was introduced in curl in 2013 with the commit series that started
with [19a05c908f7d8b](

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2022-22576 to this issue.

CWE-305: Authentication Bypass by Primary Weakness

Severity: Medium


- Affected versions: curl 7.33.0 to and including 7.82.0
- Not affected versions: curl < 7.33.0 and curl >= 7.83.0

Note that libcurl is used by many applications, but not always advertised as


A [fix for CVE-2022-22576](


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

  A - Upgrade curl and libcurl to version 7.83.0

  B - Apply the patch to your version and rebuild

  C - Set the bearer string as password *as well* when using OAUTH2 bearer
      authentication with these protocols.


It was first reported to the curl project on March 18 2022. We contacted
distros@...nwall on April 18.

libcurl 7.83.0 was released on April 27 2022, coordinated with the
publication of this advisory.


Reported and patched by Patrick Monnerat.

Thanks a lot!


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