CVE-2025-57816: Ethyca Fides Rate Limiting DoS Vulnerability

CVE-2025-57816 Overview

CVE-2025-57816 affects Ethyca Fides, an open-source privacy engineering platform. Versions prior to 2.69.1 implement ineffective IP-based rate limiting in the Fides Webserver API. The system applies rate limits using the directly connected infrastructure IP rather than the originating client IP, and stores counters in process memory instead of a shared store. Attackers can bypass intended rate limits when Fides runs behind a CDN, proxy, or load balancer, leading to potential denial of service. The flaw is tracked under CWE-799: Improper Control of Interaction Frequency.

Critical Impact

Attackers can circumvent built-in API rate limits in multi-instance or proxied deployments and exhaust resources, causing denial of service.

Affected Products

• Ethyca Fides versions prior to 2.69.1
• Deployments using Fides built-in rate limiting behind CDNs, reverse proxies, or load balancers
• Multi-replica Fides Webserver deployments without a shared counter store

Discovery Timeline

• 2025-09-08 - CVE-2025-57816 published to NVD
• 2025-09-10 - Last updated in NVD database

Technical Details for CVE-2025-57816

Vulnerability Analysis

The Fides Webserver API enforces request rate limiting by counting requests per source IP address. Two design defects break this control in production deployments. First, the application reads the IP from the directly connected peer rather than parsing forwarded headers such as X-Forwarded-For. When Fides sits behind a CDN, ingress controller, or load balancer, every request appears to come from a small set of infrastructure IPs. Second, the limiter stores counters in process-local memory. In horizontally scaled deployments with multiple Fides replicas, each worker maintains an independent counter. Requests distributed across replicas reset effectively, so the aggregate request rate exceeds the per-instance threshold without triggering enforcement.

Root Cause

The root cause is improper control of interaction frequency [CWE-799]. The rate limiter trusts the transport-layer source address and lacks a shared backend such as Redis to coordinate counters across processes. Deployments relying on external rate limiting through a Web Application Firewall (WAF) or API gateway are not affected.

Attack Vector

An unauthenticated attacker sends high-volume requests to public Fides API endpoints. Because counters reset per replica and infrastructure IPs are shared across all clients, the attacker bypasses the intended throttle and consumes CPU, memory, and downstream database resources, producing a denial-of-service condition against the privacy management plane.

The maintainers' fix introduces an Nginx load balancer configuration in front of multiple Fides webserver instances and adjusts development tooling to support that topology:

events {}

http {

  log_format upstream_log '$remote_addr - $remote_user [$time_local] '
                        '"$request" $status $body_bytes_sent '
                        '"$http_referer" "$http_user_agent" '
                        'upstream_addr="$upstream_addr" '
                        'upstream_status="$upstream_status"';

  upstream fides {
    server fides-1:8080;
    server fides-2:8080;
  }

  server {
    listen 8080;
    access_log /dev/stdout upstream_log;

    location / {
      proxy_pass http://fides;
    }
  }
}

Source: ethyca/fides commit 59903c1

Detection Methods for CVE-2025-57816

Indicators of Compromise

• Sustained spikes in request volume to Fides API endpoints originating from a narrow set of upstream proxy or CDN IPs
• Elevated 4xx/5xx response rates and increased response latency on the Fides Webserver
• CPU or memory saturation on Fides webserver replicas without proportional rate-limit rejections in logs

Detection Strategies

• Compare request rates recorded at the WAF or load balancer with rate-limit rejections logged by Fides; large discrepancies indicate bypass.
• Aggregate X-Forwarded-For client IPs at the proxy tier and alert on per-client request rates exceeding policy thresholds.
• Track Fides version inventory and flag any instance running a release earlier than 2.69.1.

Monitoring Recommendations

• Enable upstream access logging on the reverse proxy, including $remote_addr and $upstream_addr, to attribute traffic to true client IPs.
• Forward Fides and proxy logs into a SIEM or data lake to correlate API abuse patterns across replicas.
• Monitor pod or container resource metrics for the Fides Webserver and alert on sustained saturation.

How to Mitigate CVE-2025-57816

Immediate Actions Required

• Upgrade Fides to version 2.69.1 or later, which addresses the rate limiting deficiency.
• Deploy an external rate-limiting layer such as a WAF, API gateway, or Nginx in front of Fides if upgrading is delayed.
• Audit deployments for direct exposure of Fides webserver replicas and place all instances behind a controlled ingress.

Patch Information

The fix is delivered in Fides 2.69.1. See the GitHub Security Advisory GHSA-fq34-xw6c-fphf, the GitHub Release 2.69.1, and the remediation commit 59903c1.

Workarounds

• Implement rate limiting externally at the infrastructure tier using a WAF or API gateway keyed on the true client IP.
• Configure reverse proxies to enforce per-client request quotas based on X-Forwarded-For rather than relying on the application limiter.
• Restrict access to the Fides API to known networks where feasible to reduce the attack surface.

# Example Nginx rate limit keyed on real client IP via X-Forwarded-For
http {
  map $http_x_forwarded_for $client_ip {
    "~^(?P<first>[^,]+)" $first;
    default              $remote_addr;
  }

  limit_req_zone $client_ip zone=fides_api:10m rate=10r/s;

  upstream fides {
    server fides-1:8080;
    server fides-2:8080;
  }

  server {
    listen 8080;
    location / {
      limit_req zone=fides_api burst=20 nodelay;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_pass http://fides;
    }
  }
}