The vulnerability is in Bun versions before 1.3.5. The package manager’s default trust allow list can be spoofed by a non‑npm package that shares a name with a trusted entry. An attacker can therefore have a malicious package impersonated as a trusted npm package, allowing it to be downloaded and executed during the installation process. This undermines the integrity of the dependency chain and may result in arbitrary code execution within the environment that runs Bun.

Affected product is Bun itself. All installations using versions prior to 1.3.5 are vulnerable, regardless of operating system, because the defect is in the core dependency resolver.

The CVSS score of 5.9 indicates moderate risk, while an EPSS score of less than 1% shows a low likelihood of exploitation. The vulnerability is not listed in CISA’s KEV catalog. A likely attack vector involves an attacker placing a malicious package with a name matching a trusted npm entry into a repository or file system that Bun resolves, thereby hijacking the dependency resolution path. Successful exploitation could lead to arbitrary code execution as the user running Bun.