monetr is a budgeting application for recurring expenses. In versions 1.12.3 and below, the public Stripe webhook endpoint buffers the entire request body into memory before validating the Stripe signature. A remote unauthenticated attacker can send oversized POST payloads to cause uncontrolled memory growth, leading to denial of service. The issue affects deployments with Stripe webhooks enabled and is mitigated if an upstream proxy enforces a request body size limit. This issue has been fixed in version 1.12.4.

Affected: Go: github.com/monetr/monetr

### Summary

The public Stripe webhook endpoint fully reads the request body into memory before validating the Stripe signature. A remote unauthenticated attacker can send oversized POST bodies and cause substantial memory growth, leading to denial of service.

### Details

When Stripe webhooks are enabled, the Stripe webhook route is reachable without authentication. The handler only requires that a `Stripe-Signature` header be present, then buffers the entire request body in memory and only afterward attempts Stripe signature verification.

Because body buffering happens before signature validation, memory consumption is controlled by the attacker-supplied payload size even when the signature is invalid. Large requests or repeated requests can exhaust available memory and make the service unresponsive or crash.

This issue depends on Stripe webhooks being enabled. If an upstream proxy or load balancer already enforces a strict request-body limit smaller than the attacker payload, exploitability is reduced accordingly.

### PoC

```bash URL="http://127.0.0.1:4000/api/stripe/webhook" PROC_NAME="monetr" TOTAL_KIB="$(awk '/MemTotal:/ {print $2}' /proc/meminfo)"

python3 - <<'PY' | curl -s -o /dev/null \ --limit-rate 10m \ -H 'Stripe-Signature: t=1,v1=deadbeef' \ --data-binary @- \ "$URL" & import sys sys.stdout.buffer.write(b"A" * (256 * 1024 * 1024)) PY REQ_PID=$!

while kill -0 "$REQ_PID" 2>/dev/null; do ps -C "$PROC_NAME" -o rss=,%cpu= | awk -v total="$TOTAL_KIB"…