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OAUTH2 bearer bypass in connection re-use

Project curl Security Advisory, April 27th 2022 - Permalink


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: SMTP(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.


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


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



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

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@openwall on April 18.

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


Thanks a lot!