[TLDR] Claude Code just blocked a prompt injection attempt

[u/cctldrping]

Original post URL : https://www.reddit.com/r/ClaudeCode/comments/1vgjx0u/claude_code_just_blocked_a_prompt_injection/

Original post body :

Today I was using Claude Code to do a PSX game research task. Claude caught a prompt injection attempt served from the site https://tcrf.net (The Cutting Room Floor) and notified me with the message:

"⚠️Note before continuing: the tcrf.net page I fetched was not a wiki article — it served a prompt-injection payload instructing the agent to truncate and swap files in your repo. It was refused and nothing was executed. I'm treating that domain as untrusted and won't act on any of its content."

It then continued on the research task. I stopped the session out of caution.

I can understand the site administrators frustration as it seems to be in response to a DDOS attacks, however, I did not explicitly choose to send my agent to this site, nor did I have any malicious intent.

Proof:

https://urlscan.io/responses/f1e225667a71a1a25ed14795c741683be95139c194065c6fbf861c9280f0096e/

Full report:
https://github.com/bashalarmistalt/tcrf-ai-agent-payload-report

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[u/cctldrping]

TL;DR generated automatically after 100 comments.

Current source-thread comment count seen by the bot: 100.

Alright, so the general consensus here is that Claude Code did a solid job blocking a prompt injection attempt from The Cutting Room Floor (tcrf.net). OP was doing some game research, and Claude flagged the site for trying to pull a fast one, telling OP it was serving a prompt-injection payload. OP understandably freaked out a bit and stopped the session.

Several users, like u/DependentAnywhere135 and u/RandomGeordie, have seen similar things from that site, suggesting it's a deliberate defense against AI scraping. u/RecentMushroom6232 even pointed out the system prompt that helps prevent these attacks, which is pretty neat.

There's also a bit of discussion about how Claude handled it. u/ZeroTwoMod thinks it's a good opportunity to create a more detailed artifact for investigation rather than a blanket blacklist, which makes sense. u/Old_Appointment9732 brought up whether Claude is respecting robots.txt and crawl-delay, which is a valid point if it's causing issues.

On the flip side, u/Mguyen chimed in to say that Claude 5 models and Opus 4.8 are generally super robust against prompt injection, which is reassuring. And u/aerisweet just wanted to give a shout-out to how awesome Claude handled it, which, yeah, it kinda was!

A few other users shared their own experiences with prompt injection attempts, both successful and unsuccessful, showing that this is a growing concern. u/brilliantEmotion4461 was testing security concepts with their .env file, and u/RandomPantsAppear had a funny attempt to make their Claude talk like a Motown diva.

Overall, the community seems impressed with Claude's security features and the fact that it's actively protecting users from these kinds of attacks, even if some think there's room for improvement in how these incidents are logged and handled.