The Glass House: Shattering IBM Db2 with a Single SELECT

IBM Db2 is a beast. It's the kind of database engine designed to survive nuclear winters, running critical workloads for banks and governments where 'downtime' is a dirty word. It is complex, ancient, and generally robust. But software architecture teaches us a cruel lesson: complexity is the enemy of security. In this case, the vulnerability isn't a complex buffer overflow requiring heap feng shui; it's a logic flaw in how the engine handles its own appetite.

IBM refers to the crash condition as a "trap." In Db2 parlance, a trap isn't an ambush set by an attacker; it's the engine realizing it has entered an undefined state—usually a segmentation fault (SIGSEGV) or an illegal instruction—and intentionally terminating the db2sysc process to prevent data corruption. It's a fail-safe. The problem? A low-privileged user can force the engine to pull this rip-cord on demand.

Imagine a skyscraper equipped with a self-destruct mechanism that triggers if the fire alarm system gets confused. Now imagine giving the button for that mechanism to the intern on the second floor. That is CVE-2025-36070. It turns the database's defensive programming against itself, transforming availability into a fragility.

The vulnerability is categorized under CWE-770: Allocation of Resources Without Limits or Throttling. In the context of a relational database engine, this usually points to the Query Optimizer or the Runtime Interpreter. When you send a SQL query (SELECT * FROM ...), the engine builds a query plan. It allocates memory structures for sorting, joining, and retrieving rows. If the table structure is exotic—think deep recursion, complex partitioning, or specific LOB (Large Object) handling—the engine might miscalculate the resources needed.

In this specific case, the flaw is triggered when selecting from "certain types of tables." While IBM is famously opaque about the specifics (likely to prevent mass chaos before patching), the symptoms point to a stack exhaustion or an unchecked allocation loop. The engine attempts to process the table metadata or the row structure, allocates resources (likely on the stack or a specific memory heap), and fails to check if it has hit a limit.

Instead of failing gracefully—returning a SQL0973N (Not enough storage) or SQL0101N (Statement too long) error—the underlying C++ code encounters a violation. The OS signals a fault, the Db2 signal handler catches it, dumps a stack trace (the "trap file"), and kills the instance. The lack of bounds checking transforms a heavy query from a performance problem into a catastrophic availability event.

Because IBM Db2 is proprietary, closed-source software, we don't have the luxury of a GitHub diff to dissect. However, based on the behavior (Trap via CWE-770), we can reconstruct the likely culprit in the engine's pseudo-code. The vulnerability likely resides in a recursive function handling table definitions or row deserialization.

The Vulnerable Pattern (Reconstructed):

// Hypothetical Vulnerable Logic in Query Interpreter
void ProcessTableStructure(TableMetadata* table, ResourcePool* pool) {
    // No depth check or resource limit check here
    if (table->hasComplexAttribute()) {
        // Recursive call or massive allocation based on user-controlled structure
        size_t sizeNeeded = CalculateSize(table);
        
        // DANGER: Allocating without checking pool limits or stack depth
        void* buffer = pool->allocate(sizeNeeded);
        
        if (!buffer) {
            // In a robust system, we throw an exception here.
            // in the vulnerable version, we might dereference NULL 
            // or the allocation itself triggers a stack overflow.
            throw FatalEngineError("Trap: SIGSEGV"); 
        }
        
        ProcessTableStructure(table->nextChild, pool);
    }
}

The Robust Logic (The Fix):

The fix involves introducing "throttling" or "guard rails." The engine must check if the request exceeds safety margins before attempting the operation.

// Patched Logic
void ProcessTableStructure(TableMetadata* table, ResourcePool* pool, int depth) {
    // 1. Enforce Recursion Limits
    if (depth > MAX_RECURSION_DEPTH) {
        throw SqlException(SQL_CODE_LIMIT_EXCEEDED, "Table structure too complex");
    }
 
    // 2. Enforce Allocation Limits
    size_t sizeNeeded = CalculateSize(table);
    if (sizeNeeded > MAX_SAFE_ALLOCATION) {
        throw SqlException(SQL_CODE_MEMORY_LIMIT, "Resource request too large");
    }
 
    void* buffer = pool->allocate(sizeNeeded);
    // ... processing continues safely ...
}

The difference is subtle but critical. The vulnerable code blindly trusts that the table structure won't exhaust the system's limits. The fixed code assumes the worst and validates the cost before spending the currency.

Exploiting this does not require binary ninjutsu; it requires SQL. The barrier to entry is extremely low: you just need a valid account. This could be a developer, a data analyst, or a service account with CONNECT and SELECT privileges. The attack vector is strictly internal or exposed via a web application that allows flexible querying (e.g., a reporting dashboard).

The Attack Chain:

1. Reconnaissance: The attacker enumerates table types. They are looking for specific structures hinted at in the advisory. This might be system catalog tables, tables with XML columns, or recursive views.
2. Triggering the Crash: The attacker executes a query designed to traverse the vulnerable structure.

-- Concept of the attack query
-- This looks normal, but targets the "poison" table structure
SELECT * FROM SCHEMA.VULNERABLE_TABLE_TYPE;

3. The Result:
   • The user's connection hangs immediately.
   • The database administrator sees the connections drop.
   • The db2diag.log fills with panic: DIA8300C A signal "SIGSEGV" was received.
   • The instance goes down. All transactions roll back. The business stops.

This is a classic "Logic DoS." Unlike a flood attack (DDoS), which requires bandwidth, this requires a single packet containing a specific request. It is silent until it is fatal.

Mitigation for Db2 is rarely as simple as apt-get upgrade. These are heavy installations, often requiring scheduled downtime. However, given the severity (Availability: High), this cannot be ignored. The flaw exists in the core engine (db2sysc), so there is no configuration tweak or firewall rule that can reliably filter the specific SQL causing the crash without blocking legitimate traffic.

Remediation Steps:

1. Identify Vulnerable Instances: Check versions. Db2 11.5.x up to 11.5.9 and 12.1.0 through 12.1.2 are vulnerable.
2. Apply Special Builds: IBM has released "Special Builds" (hotfixes) because standard fix packs take longer to validate.
   • For 11.5.9: Apply Special Build #66394 (APAR DT440126).
   • For 12.1.x: Upgrade to v12.1.3 or apply Special Build #72296.
3. Monitor Logs: Until patched, setup alerts on db2diag.log for the keyword TRAP. While this won't stop the crash, it will tell you why your phone is ringing at 3 AM.

Since no workarounds exist, the only path forward is binary replacement. Security teams should push for expedited patching windows, citing the low complexity of exploitation.