Description

The wpForo Forum WordPress plugin from 3.0.0 before 3.1.6 does not verify the source of client-supplied IP address headers before using them to key its per-visitor rate limit on paid AI requests, allowing unauthenticated attackers to bypass the limit by spoofing the header and exhaust the site owner's metered AI credits.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.3",
  "pubDate": "2026-09-25T09:17:06.093Z",
  "pubdate": "2026-09-25T09:17:06.093Z",
  "executiveSummary": "The wpForo Forum WordPress plugin (versions 3.0.0 through 3.1.5) contains a critical architectural flaw regarding its rate-limiting mechanism for AI-integrated features. The vulnerability is classified as an improper verification of client-supplied HTTP headers, specifically those used for identifying source IP addresses.\nBy failing to sanitize or validate the integrity of headers such as 'X-Forwarded-For' or similar proxy-based identifiers, the plugin allows unauthenticated remote attackers to spoof their origin IP address. This enables the bypass of per-visitor rate limits enforced on paid AI-assisted requests.\nThe primary business risk is the potential for resource exhaustion of the site owner's metered AI service credits. An attacker can orchestrate automated requests that appear to originate from unique IP addresses, effectively bypassing security controls that are designed to mitigate automated abuse. This leads to direct financial loss through credit depletion and potentially service denial if the platform's AI quota is exhausted. The vulnerability requires no authentication and can be exploited over any network interface exposed to the plugin's functionality.",
  "technicalDetails": "The vulnerability resides in the core logic used by wpForo to track and restrict per-visitor usage of its AI-powered features. The plugin relies on client-provided headers—typically headers meant to identify the original client IP behind a proxy—to determine the identity of a requester for rate-limiting purposes. Because the application logic accepts these headers as authoritative without verifying if the request actually traversed a trusted proxy, it becomes susceptible to source spoofing.\nThe root cause is an improper trust relationship in the implementation of the IP retrieval mechanism. Instead of relying on the immutable 'REMOTE_ADDR' server variable, which reflects the immediate source of the connection, the plugin retrieves IP addresses from HTTP headers that are easily manipulated by the client.\nThe attack flow proceeds as follows: An unauthenticated attacker initiates an HTTP request to the wpForo endpoint responsible for AI-based functionality. The attacker injects a spoofed header (e.g., 'X-Forwarded-For: [Random_IP]') into the request payload. The plugin extracts this value and uses it as the primary identifier to query its internal rate-limiting cache. Since each spoofed IP appears as a new, unique user, the rate-limiting logic resets or fails to increment the counter for the malicious actor.\nThis behavior facilitates a trivial bypass of security thresholds. An attacker can cycle through thousands of spoofed IP addresses in a rapid automated fashion, consuming the site owner's metered API credits for AI services. This mechanism does not require a large botnet, as the attacker's actual IP address is masked and the application perceives each request as originating from a different entity.\nThe affected component is the plugin's request handling and validation middleware for AI services. Affected versions include 3.0.0 up to, but not including, 3.1.6. The exploitation is remote, requires no prior authentication or administrative privileges, and is inherently effective against any public-facing installation utilizing the plugin's AI features. Post-exploitation, the impact is strictly limited to the exhaustion of service quotas and the associated financial liability, although it demonstrates a failure in secure input handling that could lead to other forms of application-level abuse if left unpatched."
}