Researcher says Bun's trusted install check can be bypassed through .bin links

Security researcher X3r0Day reported on November 6 that Bun rejected an install-time code execution issue as invalid, then shipped a partial fix in Bun 1.4.4 while a second variant remained exploitable. Bun told the researcher that bin linking "has nothing to do with trustedDep" and was "not a bun issue," and the researcher's BunnyHijack-PoC demonstrates that an untrusted bin entry placed on PATH delivers install-time execution the trustedDependencies gate was meant to prevent. Bun, which is Anthropic-owned, said trustedDependencies was only ever intended to govern lifecycle scripts, leaving CI pipelines, scanners and automated updaters that install code without running the application exposed.

Researcher says Bun's trusted install check can be bypassed through .bin links X3r0Day says a rejected bin-linking report still yields install-time code execution on Bun 1.4.4 through a trusted package's postinstall script. By Ryan Merket https://runtimewire.com/author/ryan-merket · Published · Updated Primary source: x.com https://x.com/X3r0DaySec/status/2118721688955490645 Why it matters Bun is Anthropic-owned infrastructure used to distribute and run Claude Code-era developer tooling. Its install-time trust boundary affects CI pipelines, scanners and automated updaters that install code without running the application. Bun says trustedDependencies was only ever about lifecycle scripts, while the PoC argues an untrusted bin entry placed on PATH delivers the install-time execution the gate was built to prevent. Security researcher X3r0Day @X3r0DaySec https://x.com/X3r0DaySec said on November 6th that Bun rejected a reported install-time code execution issue as invalid, then shipped a change in Bun 1.4.4 for part of the behavior while leaving another variant working. In a thread on X https://x.com/X3r0DaySec/status/2118721688955490645 , X3r0Day said Bun told the researcher that bin linking "has nothing to do with trustedDep" and was "not a bun issue." The researcher's public proof of concept, BunnyHijack-PoC https://github.com/X3r0Day/BunnyHijack-PoC , describes a gap in the trust boundary… When you purchase through links in our articles, we may earn a small commission https://runtimewire.com/affiliate-monetization-standards . This doesn’t affect our editorial independence.