I got into YC by hacking it
A founder exposed a critical vulnerability in Y Combinator's new AI-powered Paxel scoring system, designed to evaluate Startup School applicants based on their coding activity. After initially being ignored, his public disclosure prompted YC to swiftly patch the flaw and invite him to Startup School. This narrative of technical prowess, responsible disclosure, and a major incubator's reaction resonated deeply with the HN community.
The Lowdown
Obaid, a founder applying to Y Combinator's Startup School, discovered a significant security flaw in Paxel, a new YC-developed tool that uses AI to analyze applicants' coding work. The tool, which involved a curl | bash script to install a Dockerized Ruby application, was designed to score founders across five axes (e.g., engineering quality, product thinking) based on their chat transcripts and code commit histories.
- Paxel processed applicants' coding sessions through a YC-sponsored GPT-5.5 proxy, returning scores and notes. However, it used a nonce without proper cryptographic signing.
- This meant that while the nonce itself was validated, the actual scores and descriptive text returned by the LLM could be arbitrarily altered by the applicant before being uploaded to YC's servers.
- Obaid demonstrated this vulnerability by creating "paxel-boosted," a tool that allowed users to forge higher scores and notes.
- After privately disclosing the bug with no immediate response, Obaid made his findings public. Within hours, Jared Friedman of YC acknowledged the issue, announced a patch, and invited Obaid to Startup School.
The story highlights the critical importance of foundational security principles in distributed systems, especially when dealing with sensitive data and AI-driven assessments. YC's prompt and positive response to the responsible disclosure was widely praised.
The Gossip
Paxel's Perilous Practices
Many users expressed serious concerns about YC's Paxel tool, particularly its invasive `curl | bash` installation method, system-level access, and the potential transfer of sensitive IP (e.g., code edit diffs) to third-party AI services. The discovery of a basic web security flaw in such a system heightened fears regarding data privacy and the future of technical hiring practices.
YC's Yielding to Ingenuity
Commenters largely lauded YC's swift and positive response to the vulnerability disclosure, interpreting it as an endorsement of resourceful, 'hacker' mindsets. This aligns with YC's historical appreciation for creative problem-solving, even if the 'hack' was technical rather than 'non-computer,' a distinction previously made in YC applications.
AI Assessments Under Attack
The discussion extensively questioned the fundamental concept of using AI to score founder potential, labeling Paxel's approach as 'dumb' and easily gamed. Critics worried about the reliability of 'secret metrics,' the privacy implications of feeding personal coding data to an AI, and whether such systems could ultimately lead to 'brand damage' for YC.
Semantic Splits on 'YC Acceptance'
A recurring point of clarification revolved around the story's title claiming 'getting into YC.' Many users pointed out that the invitation was specifically for Startup School, a distinct program from the more selective main YC accelerator, suggesting a more precise title was warranted to avoid confusion.