CVE-2023-27533: Input Validation

A vulnerability in input validation exists in curl <8.0 during communication using the TELNET protocol may allow an attacker to pass on maliciously crafted user name and "telnet options" during server negotiation. The lack of proper input scrubbing allows an attacker to send content or perform option negotiation without the application's intent. This vulnerability could be exploited if an application allows user input, thereby enabling attackers to execute arbitrary code on the system.

cURL libcurl could allow a remote attacker to bypass security restrictions, caused by a TELNET option IAC injection flaw. By sending a specially crafted request, an attacker could exploit this vulnerability to pass on user name and "telnet options" for the server negotiation.

— IBM

curl supports communicating using the TELNET protocol and as a part of this it offers users to pass on user name and "telnet options" for the server negotiation. Due to lack of proper input scrubbing and without it being the documented functionality, curl would pass on user name and telnet options to the server as provided. This could allow users to pass in carefully crafted content that pass on content or do option negotiation without the application intending to do so. In particular if an application for example allows users to provide the data or parts of the data.

— Red Hat