A vulnerability? Yes. A serious one... i don't really think so in the grand scheme of things. Injection vulnerabilities in one form or another are like 90% of all security vulnerabilities. We have the obvious ones like sql injection or shell injection. We dont call XSS injection but it really is just html/js injection. Even things like buffer overflows are injections if viewed through the right lens. If there is one…
For all of those other injection attacks we know what the mitigations are: parameterized queries for SQL injection. Context-aware HTML escaping for XSS. Shell special character escaping for shell commands.
Prompt injection does not have a reliable mitigation yet. It's currently an injection attack without a fix.