# Apache Doris — CWE-407 Disclosure Brief

**Project:** Apache Doris
**Disclosure date:** 2026-03-27
**Severity:** MEDIUM
**Speedup:** 2.5×
**Status:** PATCHED

---

## Finding

Apache Doris's `BindExpression` rule in the Nereids query optimizer calls `groupingExprs.contains()` on a `List` inside a loop over aggregate expressions in non-`FULL_GROUP_BY` mode. For P aggregate expressions each checked against G grouping expressions, this is O(P×G) per query binding pass. The defect is in the expression analysis hot path that runs for every aggregation query.

## The Defect(s)

| ID | Location | Pattern | Complexity |
|----|----------|---------|------------|
| doris-0001 | `nereids/rules/analysis/BindExpression.java` | `groupingExprs.contains()` O(P×G) per aggregate in non-FULL_GROUP_BY mode | O(P×G) |

## Complexity Proof

Let P = number of aggregate output expressions, G = number of grouping expressions in the GROUP BY clause.

During expression binding in non-`FULL_GROUP_BY` mode, `BindExpression` iterates over all P aggregate output expressions. For each, it calls `groupingExprs.contains(expr)` where `groupingExprs` is a `List` — an O(G) linear scan:

```
For agg_expr_1: groupingExprs.contains() scans G entries
For agg_expr_2: groupingExprs.contains() scans G entries
...
For agg_expr_P: groupingExprs.contains() scans G entries
Total: P × G comparisons per query binding
```

Pre-building `Set<Expression> groupingSet = new HashSet<>(groupingExprs)` before the aggregate loop reduces each check to O(1):

```
Fixed: build O(G) + P × O(1) = O(G + P)
Speedup: G× at the inner check; net ~2.5× for typical P/G ratios
```

For P = 25 aggregate expressions and G = 10 grouping expressions, the defective path performs 250 expression comparisons; the fixed path performs 10 (set build) + 25 (lookups) = 35.

## Impact

All Apache Doris queries using non-`FULL_GROUP_BY` aggregation with a meaningful number of SELECT expressions are affected. This covers a large fraction of analytical SQL queries — reporting queries with many measured dimensions, BI tool-generated SQL with complex GROUP BY clauses, and ad-hoc analytical queries on Doris tables. The defect is in the Nereids optimizer's expression binding phase, which runs before cost-based optimization; query planning latency increases with P×G for every affected query. Interactive analytics workloads and high-QPS reporting dashboards are most sensitive to optimizer latency.

## The Fix

Before the aggregate expression iteration loop in the relevant `BindExpression.bind()` method path, build a `HashSet<Expression>` from `groupingExprs`. Replace `groupingExprs.contains(expr)` with `groupingSet.contains(expr)` throughout the loop body.

## Patch

```diff
  private Plan bindAggregate(MatchingContext<LogicalAggregate<Plan>> ctx) {
      List<Expression> groupingExprs = aggregate.getGroupByExpressions();
+     Set<Expression> groupingSet = new HashSet<>(groupingExprs);
      List<NamedExpression> outputExprs = aggregate.getOutputExpressions();

      for (NamedExpression outputExpr : outputExprs) {
-         if (!groupingExprs.contains(outputExpr)) {
+         if (!groupingSet.contains(outputExpr)) {
              // validate non-grouping aggregate reference
          }
      }
  }
```

## What We Ask

Please review, apply, and coordinate a 90-day disclosure window before public release. Reply to security@undefect.com.

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*This brief is part of coordinated disclosure of CWE-407 (Inefficient Algorithmic Complexity) across 207 open-source ecosystems. Full report: https://undefect.com*
