CVE-2026-91968

# Unbounded nested task-filter recursion permits API process termination ## Summary Authenticated task-list routes accept a filter expression without a length or nesting-depth bound, preprocess it, parse it recursively through fexpr, and recursively convert the resulting expression tree. A syntactically valid deeply nested expression well below the HTTP request-size ceiling exhausts memory and kills the API process. ## Impact and affected scope - **Type:** Resource Exhaustion Recursive Parser - **Affected component:** GET /api/v2/projects/{project}/tasks?filter=<nested expression>; Other authenticated task-collection entrypoints that share getTaskFiltersFromFilterString - **Preconditions:** A low-privileged authenticated user supplies thousands of balanced parentheses around a valid task predicate in the filter query parameter. - **Verified revision:** `349cd5adbcc831ef08b08e6c9c6d627603c39606` on 28 August 2026 - **Affected release range:** `= 2.5.0`; broader historical range not established and maintainer confirmation requested A single low-privileged network request can terminate the API process and deny service to all users. ## Technical details The server preprocesses and recursively parses/traverses an unbounded filter expression without rejecting excessive length or depth. Attack path: Authenticate, request an accessible project's task collection with 20,000 nested parenthesis pairs around id = 1, and drive parser and expression-tree memory growth until the process is killed. Relevant code: - `pkg/models/task_collection_filter.go:240` - `pkg/models/task_collection_filter.go:268` - `pkg/models/task_collection_filter.go:274` - `pkg/models/task_collection_filter.go:276` - `pkg/models/task_collection_filter.go:295` ## Reproduction Run this only against an authorized disposable environment. The complete verified minimum file set is reproduced below. It starts the isolated target, runs the security-relevant trigger, verifies an objective target/applicat