SurrealDB: Denial of Service via deep operator chains — surrealdb
Uncontrolled RecursionAn authenticated user could crash a SurrealDB server with a single query containing a long chain of operators.
Such a query — for example RETURN 1 + 1 + 1 + ... with tens of thousands of terms — is parsed into an expression tree one level deep per operator. Because the chain is flat and the pratt parser appends to it iteratively, the configured query- and object-recursion limits never fire, so the tree grows unbounded with the length of the query.
The root cause: the over-deep tree is later walked recursively, one call per node, when it is dropped, formatted, or lowered for execution — overflowing the thread stack and aborting the process.
Impact
An authenticated user with query-execution privileges can crash a SurrealDB server with a single query containing a long chain of operators. The whole process aborts, denying service to every namespace and database on that instance until it is restarted. The crash occurs during query processing, before any data is read or written (availability only).
Patches
A patch introduces a dedicated expression-depth budget — expr_recursion_limit, sourced from max_expression_parsing_depth (default 128, configurable via SURREAL_MAX_EXPRESSION_PARSING_DEPTH). It is charged once per pratt-parser level and once per operator appended to the spine, so an over-deep operator chain is rejected with a syntax error instead of building a tree that overflows the stack downstream. Paths that re-parse already-validated stored data are exempted, so existing databases with deep stored expressions still load.
- Versions 3.1.5 and later are not affected by this issue.
Workarounds
Users unable to patch should consider the following workarounds:
- Restrict the ability of untrusted users to execute arbitrary queries via the
--deny-arbitrary-querycapability flag for the affected user classes (guest, record, or system). - Restrict untrusted access to the WebSocket
/rpcendpoint, which accepts larger request bodies than the HTTP/sqlendpoint. The/sqlendpoint's 1 MiB body limit lowers the achievable operator depth but does not by itself guarantee the stack cannot be exhausted. - Run SurrealDB under an orchestrator or process manager that restarts it automatically on exit (e.g. Kubernetes, systemd
Restart=on-failure, or a Docker restart policy), so the server recovers immediately after a crash. This limits downtime from a successful attack but does not prevent the crash.
References
- SurrealQL Documentation — Operators
fix(syn): bound expression operator-tree depth to prevent stack-overflow DoS
| Software | From | Fixed in |
|---|---|---|
surrealdb
|
3.0.0 | 3.1.5 |
Deep Security Visibility Without the Complexity
SynScan provides clear, real-time security insights so you can monitor your attack surface, spot risks early, and act fast—without extra complexity.
- No setup fees
- 5-min deployment
- Cancel anytime
Frequently Asked Questions
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.