Taskcluster’s web‑server component is vulnerable to unauthenticated remote code execution when a user supplies a specially crafted GraphQL filter argument. The vulnerable code path parses the filter string with the sift library, which incorrectly evaluates expressions containing the $where operator, enabling an attacker to inject arbitrary code. An unauthenticated attacker can send a request to the exposed GraphQL endpoint and cause the server to execute code with the web‑server’s privileges, leading to full compromise of the deployment. The weakness is rooted in input validation failures, missing authentication, and insecure use of the sift library, as reflected by the associated CWE identifiers.

The flaw affects any Taskcluster deployment running a version earlier than 100.3.0 that has an anonymous role configured to expose the GraphQL endpoint. The vulnerable product is Taskcluster, an infrastructure framework maintained by Mozilla. Deployments that enable the web‑server component and permit unauthenticated GraphQL access are at risk; all other versions or those that have already applied the 100.3.0 patch are not affected.

With a CVSS score of 8.7, the vulnerability is considered high severity. The EPSS score is not available, but the lack of authentication on the GraphQL interface inherently increases exploitability: any network user that can reach the endpoint could craft the malicious filter payload. The issue is not currently listed in CISA’s KEV catalog, but the presence of unauthenticated code execution presents a high risk to exposed systems. The guardrails are straightforward: the patch in v100.3.0 removes the vulnerable sift evaluation, and disabling anonymous access mitigates the attack surface.