CVE-2023-27533

TELNET option IAC injection

Project curl Security Advisory, March 20th 2023 - Permalink

VULNERABILITY

curl supports communicating using the TELNET protocol and as a part of this it offers users to pass on username 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 username 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.

INFO

CWE-75: Failure to Sanitize Special Elements into a Different Plane

Severity: Low

AFFECTED VERSIONS

• Affected versions: curl 7.7 to and including 7.88.1
• Not affected versions: curl < 7.7 and curl >= 8.0.0
• Introduced-in: https://github.com/curl/curl/commit/a1d6ad26100bc493c7

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

SOLUTION

Only accept ASCII username and telnet options.

• Fixed-in: https://github.com/curl/curl/commit/538b1e79a6e7b

RECOMMENDATIONS

A - Upgrade curl to version 8.0.0

B - Apply the patch to your local version

C - Do your own TELNET username or option input filtering

TIMELINE

This issue was reported to the curl project on March 3, 2023. We contacted distros@openwall 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!