Eclipse Theia CVE-2026-14574

Exploitation requires the target user to actively open a workspace - either a local folder or a cloned repository - that contains a crafted .theia/settings.json or .vscode/settings.json file embedding prototype-polluting keys (__proto__, constructor, or prototype) at any nesting depth. The AT:P metric confirms a specific precondition: the malicious workspace file must be present and accessible when Theia resolves preferences. Exploitation is inherently limited by UI:A - the victim must perform the deliberate action of opening the workspace, making this a social-engineering-dependent attack requiring the attacker to first deliver a malicious workspace to the target. Remote exploitation without workspace delivery is not possible. The vulnerability does not manifest against default Theia installations with no user-supplied workspace settings files. Authentication requirements are not relevant here, as the attack surface is the local file system, not a network-exposed API.

The CVSS 4.0 score of 5.7 (Medium) is internally consistent with the threat model. AV:L confirms exploitation is scoped to the local workspace context - the attacker cannot trigger the vulnerability remotely without first delivering a malicious workspace. AT:P (attack requirements present) captures the precondition that the victim must open a crafted workspace, and UI:A mandates active user interaction. VI:H is the dominant risk driver: prototype pollution in a Node.js process can unpredictably alter conditional logic, bypass security checks, or enable privilege escalation within the IDE process depending on downstream code that trusts inherited object properties. VC:L and VA:L are consistent with the 'Information Disclosure' tag and minor process disruption potential. No CISA KEV listing exists, and E:X (exploit maturity not defined) indicates no confirmed public exploit. The realistic threat actor is a supply-chain or social-engineering attacker distributing malicious repositories to developers - a targeted rather than opportunistic scenario. The low EPSS implied by the absence of weaponized exploits and the Medium CVSS score together suggest this is a genuine but not immediately critical priority for most organizations, unless developer toolchain security is a specific concern.

An attacker publishes or shares a repository containing a .theia/settings.json file with a deeply nested __proto__ key mapping to a crafted value. A developer clones the repository and opens it in Eclipse Theia, triggering PreferenceServiceImpl.doResolve during workspace initialization, which calls PreferenceUtils.merge on the malicious settings payload. The polluted Object.prototype then causes downstream Theia code that checks inherited properties to behave unexpectedly - potentially bypassing access checks within plugins, leaking configuration data, or altering file-system operation logic within the IDE process. No public proof-of-concept has been identified at time of analysis.