Use After Free in Cockroachdb

CockroachDB is written primarily in Go, but its storage engine relies on cgo bindings to RocksDB, a C++ library. A Use‑After‑Free (UAF) can occur when Go code holds a pointer to a RocksDB object after the underlying C++ resource has been released, and then attempts to read or write through that pointer. Because Go’s garbage collector does not manage C‑allocated memory, the responsibility for lifetime management falls on the cgo boundary.

Typical code paths where this can happen include:

• Closing a RocksDB DB* handle while an active iterator (Iterator*) is still being used by a Goroutine.
• Reusing a WriteBatch* after it has been passed to DB::Write and the batch’s internal memory has been freed by RocksDB.
• Passing a pointer to a RocksDB Snapshot* to a Go function after the snapshot has been released, then reading from it.

If an attacker can trigger one of these code paths via a SQL statement or an API request (for example, by causing a long‑running scan that holds an iterator while another connection issues a DROP TABLE that closes the underlying store), the resulting UAF may lead to memory corruption, process crash, or, in the worst case, arbitrary code execution. This maps to CWE‑416: Use After Free, and has been observed in similar storage engines (e.g., CVE‑2020‑15257 in etcd’s BoltDB usage).

Detecting a UAF in a running CockroachDB instance relies on observing abnormal behavior that stems from memory corruption. Indicators include:

• Unexpected SIGSEGV or SIGBUS signals in the CockroachDB logs, often accompanied by a stack trace that points into rocksdb symbols.
• Intermittent query failures with messages like "invalid argument" or "corruption detected" that cannot be explained by schema or data issues.
• Performance degradation or sudden increases in latency that correlate with specific workloads (e.g., repeated SELECT scans followed by DROP statements).

Because the issue lies in the native layer, traditional API scanners cannot directly see the memory corruption, but they can surface symptoms through the API. middleBrick’s black‑box scan sends a series of crafted requests that exercise common storage pathways (scans, writes, schema changes) and monitors for error responses, latency spikes, or non‑HTTP error codes that suggest a crash. For example:

# CLI usage
middlebrick scan https://cockroachdb-prod.example.com

The scan will return a finding under the "Input Validation" or "Data Exposure" category with a severity of "high" if it detects repeated 502/504 responses or crash‑like behavior after a sequence of requests that open iterators and then issue schema‑modifying statements. The finding includes remediation guidance pointing to the need to review iterator lifetime management in any custom extensions or driver code that interacts with CockroachDB’s storage layer via cgo.

Fixing a UAF in the CockroachDB codebase requires ensuring that any Go‑side reference to a RocksDB object is not used after the corresponding C++ resource has been released. The following patterns illustrate safe handling.

1. Iterators must be closed before the DB handle is closed.

func scanTable(db *rocksdb.DB, cf *rocksdb.ColumnFamilyHandle) error {
    ro := rocksdb.NewDefaultReadOptions()
    it := db.NewIteratorCF(ro, cf)
    defer it.Close() // Guarantees iterator is released
    defer ro.Destroy()

    for it.SeekToFirst(); it.Valid(); it.Next() {
        // process it.Key() and it.Value()
    }
    if err := it.Err(); err != nil {
        return err
    }
    return nil
}

func dropTable(db *rocksdb.DB) error {
    // No iterators should be alive here
    return db.DeleteCF(cf, []byte("key")) // example operation
}

2. WriteBatch lifetime must exceed the write operation.

func writeBatch(db *rocksdb.DB) error {
    wo := rocksdb.NewDefaultWriteOptions()
    batch := rocksdb.NewWriteBatch()
    defer batch.Destroy()
    defer wo.Destroy()

    batch.SetCF(cf, []byte("key1"), []byte("value1"))
    batch.SetCF(cf, []byte("key2"), []byte("value2"))
    if err := db.Write(wo, batch); err != nil {
        return err
    }
    // batch is still valid until after Write returns
    return nil
}

3. Snapshots must be released after use.

func readSnapshot(db *rocksdb.DB) error {
    ro := rocksdb.NewDefaultReadOptions()
    snap := db.NewSnapshot()
    ro.SetSnapshot(snap)
    defer snap.Release()
    defer ro.Destroy()

    it := db.NewIteratorCF(ro, cf)
    defer it.Close()
    for it.SeekToFirst(); it.Valid(); it.Next() {
        // safe reads
    }
    return it.Err()
}

When extending CockroachDB with custom Go plugins or drivers, adopt the same RAII‑style cleanup using defer statements to guarantee that RocksDB resources are released only after all dependent Go objects have finished using them. After applying these fixes, rerun the middleBrick scan to confirm that the symptom‑based findings disappear and the security score improves.