Understanding Cross-Tenant BOLA Vulnerability in stigmem-node

Overview

The stigmem-node vulnerability, identified as GHSA-x26h-xmv8-gxf7, is a cross-tenant BOLA issue that affects multi-tenant deployments using the `stigmem-plugin-multi-tenant`. This vulnerability has a CVSS score of 7.2 and is classified under CWE-639, Authorization Bypass Through User-Controlled Key.

Understanding the Vulnerability / Threat

Root Cause Analysis

The root cause of this vulnerability lies in the improper scoping of RTBF (right-to-be-forgotten) tombstones in multi-tenant stigmem nodes. There are two primary issues: 1. The `issue_tombstone` function defaults the tenant to `"default"` instead of the caller's tenant. This allows tombstones to be written to the wrong tenant. 2. The read-suppression path, specifically `_get_tombstone_filter` and `_tombstone_scope_cache`, lacks a `tenant_id` predicate. As a result, tombstone suppression is applied tenant-blind across fact queries and provenance. This vulnerability falls under the CWE-639 category, which involves authorization bypass through user-controlled keys.

Attack Surface & Vector

The attack surface for this vulnerability is limited to multi-tenant deployments of stigmem-node where the `stigmem-plugin-multi-tenant` is used. The vulnerability can be exploited via the `/v1/tombstones` endpoint and fact query/provenance read paths. An attacker must have legitimate access to the system as a tenant to exploit this vulnerability. The attack vector involves crafting requests that manipulate tenant IDs to access or modify data belonging to other tenants.

Exploitation Mechanics — Scenario Walkthrough

Scenario: Compromising Data Isolation in a Multi-Tenant stigmem-node Deployment 1. Initial Position: An attacker is authenticated as a tenant (let's call it Tenant-A) in a multi-tenant stigmem-node deployment. 2. Triggering the Flaw: The attacker crafts a request to create a tombstone for Tenant-B (another tenant on the same node) by manipulating the `tenant_id` in the request to `/v1/tombstones`. Due to the vulnerability, the tombstone is incorrectly attributed to Tenant-B but is written under the default tenant or another tenant's context. 3. What Breaks: The security boundary that is supposed to isolate Tenant-A's and Tenant-B's data is breached. The tombstone, intended to suppress reads for Tenant-B, is either not applied correctly or is applied across tenant boundaries. This leads to incorrect data visibility and undermines the RTBF mechanism. 4. Attacker's Prize: The attacker can now access or manipulate data that should be isolated to Tenant-B, compromising data-view correctness and RTBF guarantees. This could lead to unauthorized data access or manipulation, severely impacting the integrity of the system.

Real-World Impact

The real-world impact of this vulnerability is significant, especially for multi-tenant deployments. An attacker could exploit this vulnerability to: - Access sensitive data belonging to other tenants. - Manipulate data in a way that undermines the trust and isolation guarantees of the multi-tenant architecture. - Potentially disrupt service or cause data integrity issues, leading to reputational damage and legal implications.

Detection & Defense

Immediate Mitigations

The vulnerability is fixed in version `0.9.0a12` of stigmem-node. To mitigate this vulnerability, affected deployments should upgrade to this version or later. Specifically, the fix involves: - Passing `identity.tenant_id` from `issue_tombstone` into `create_tombstone`. - Adding `AND tenant_id = ?` to `_get_tombstone_filter` and `get_tombstone_status`. - Re-keying the suppression cache to include tenant. - Ensuring all read call sites thread the caller's tenant.

Detection Strategies

Defenders can detect exploitation attempts by monitoring for unusual patterns in: - Access to `/v1/tombstones` and fact query/provenance read paths. - Anomalies in data access patterns that cross tenant boundaries. - Logs indicating unauthorized access or manipulation of tombstones. Implementing SIEM rules or network signatures to detect abnormal traffic or access patterns can help identify potential exploitation attempts.

Long-Term Hardening

To prevent similar vulnerabilities in the future, consider the following long-term hardening strategies: - Implement robust access controls and tenant isolation mechanisms. - Conduct regular security audits and vulnerability assessments. - Enforce strict data access controls and monitoring. - Educate developers on secure coding practices, especially regarding tenant isolation and data access controls.

Key Takeaways

- The stigmem-node vulnerability highlights the importance of proper tenant isolation in multi-tenant architectures. - Authorization bypass through user-controlled keys (CWE-639) can have severe implications for data integrity and confidentiality. - Upgrading to version `0.9.0a12` or later is crucial for affected deployments. - Monitoring and detection strategies are essential for identifying exploitation attempts. - Long-term hardening involves implementing robust security measures and best practices.

Sources

- GitHub Security Advisories: GHSA-x26h-xmv8-gxf7