# containerd — CWE-407 Disclosure Brief
**2026-03-27 · Patch available — awaiting upstream merge**

## Finding

One O(n²) defect in containerd's OCI spec options. `filterCaps` and `WithAddedCapabilities` use `slices.Contains` (via `capsContain()`) causing O(n²) capability set processing per container launch. Patch ready for upstream review.

## The Defects

**containerd-0001 (PATCHED — HIGH):** `pkg/oci/spec_opts.go:1069,1080`

```go
// filterCaps / WithAddedCapabilities — per container launch:
func capsContain(caps []string, s string) bool {
    return slices.Contains(caps, s)  // O(n) per cap check
}
// Called inside loop over all capabilities:
for _, cap := range allCaps {
    if !capsContain(filteredCaps, cap) {  // O(n²) total
        ...
    }
}
```

`capsContain()` wraps `slices.Contains` and is called inside a loop over all capabilities. For N capabilities: **O(N²) per container launch**. Fix: `map[string]bool` capability set.

## Complexity Proof

For N capabilities (Linux has ~40 capabilities):
- Per container launch: O(N²) comparisons
- Fixed: `map[string]bool` cap set → O(N)
- At N=40: 1,600 comparisons vs 40 map lookups
- Scales with custom capability sets; notable for high container launch rate environments.

## Impact

All containerd deployments launching containers with capability filtering — virtually all production Kubernetes deployments (containerd is the default CRI). Container launches with `WithAddedCapabilities`, `WithDroppedCapabilities`, and `WithCapabilities` spec options all hit this path. Kubernetes nodes with high pod churn (auto-scalers, batch workloads, CI/CD systems) launch many containers per minute.

## The Fix

Replace `capsContain()` with a `map[string]bool` capability set:

```go
// Before
func capsContain(caps []string, s string) bool {
    return slices.Contains(caps, s)  // O(n)
}

// After
// CWE-407 fix: map[string]bool for O(1) cap check instead of O(n) slices.Contains.
func buildCapSet(caps []string) map[string]bool {
    set := make(map[string]bool, len(caps))
    for _, c := range caps { set[c] = true }
    return set
}
// Use: capSet[cap] instead of capsContain(caps, cap)
```

## Patch

`defects/containerd/patch/containerd-0001-spec-opts-cap-map.patch`

## What We Ask

1. Confirm receipt and assign a GitHub Security Advisory or issue reference.
2. Validate the patch against your OCI spec and capability test suite.
3. Assess CVE eligibility — fires on every container launch with capability filtering.
4. Coordinate a disclosure date — we are targeting 90 days from first contact.

Contact: see cover email. This brief is confidential until coordinated disclosure.
