The ON24 ScreenShare (aka DesktopScreenShare.app) plugin before 2.0 for macOS allows remote file access via its built-in HTTP server. This allows unauthenticated remote users to retrieve files accessible to the logged-on macOS user. When a remote user sends a crafted HTTP request to the server, it triggers a code path that will download a configuration file from a specified remote machine over HTTP. There is an XXE flaw in processing of this configuration file that allows reading local (to macOS) files and uploading them to remote machines.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-34823
• https://www.trustwave.com/en-us/resources/security-resources/security-advisories/
• https://www.trustwave.com/en-us/resources/security-resources/security-advisories/?fid=29105