CVE-2026-86186: AVideo API Authentication Bypass Vulnerability

CVE-2026-86186 Overview

CVE-2026-86186 is a rate-limiting bypass vulnerability in the AVideo platform API. The API skips rate-limit enforcement when incoming requests present a bot User-Agent header. Attackers exploit this logic gap by advertising themselves as a search engine crawler, disabling protections on all eight rate-limited operations. The impact includes unlimited credential brute-force attempts against the login endpoint from a single source IP. The weakness is tracked under CWE-307: Improper Restriction of Excessive Authentication Attempts.

Critical Impact
A single attacker IP can perform unlimited password guessing against any AVideo account by sending requests with a bot User-Agent string, defeating brute-force protections on the authentication API.

Affected Products

AVideo (WWBN AVideo platform)
AVideo API endpoints protected by rate limiting
AVideo authentication and login operations

Discovery Timeline

2026-09-05 - CVE-2026-86186 published to the National Vulnerability Database
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-86186

Vulnerability Analysis

The AVideo API implements rate limiting to protect eight sensitive operations, including login attempts. The enforcement logic inspects the client User-Agent header before applying throttling rules. When the header matches a known bot or crawler signature, the API bypasses rate-limit checks entirely. This exemption exists to accommodate search engine indexing, but it applies to authenticated and unauthenticated endpoints without distinction.

Attackers weaponize this behavior by attaching a common crawler User-Agent, such as one associated with a search engine bot, to malicious requests. The API then processes an unbounded number of requests from the same IP address. On the login endpoint, this enables credential stuffing and password brute-force attacks against any account without triggering lockouts or throttling.

Refer to the GitHub Security Advisory and the VulnCheck Security Advisory for the full technical write-up.

Root Cause

The root cause is an insecure allow-list in the rate-limit middleware. The middleware treats the client-supplied User-Agent header as trustworthy input and skips enforcement when it matches a bot signature. Because User-Agent strings are attacker-controlled, this control fails open. The design also applies the exemption uniformly across all eight protected operations rather than restricting it to read-only content endpoints.

Attack Vector

Exploitation requires no authentication and no user interaction. An attacker sends HTTP requests to the AVideo API login endpoint with a User-Agent header impersonating a common crawler. The rate-limit middleware evaluates the header, matches the bot signature, and forwards the request without incrementing any counter. The attacker repeats this indefinitely, iterating through password lists against a single username or spraying passwords across many accounts.

Successful exploitation yields account takeover on any credential the attacker can guess. Because the bypass operates at the middleware layer, IP-based blocklists and login-attempt counters do not trigger.

Detection Methods for CVE-2026-86186

Indicators of Compromise

High volume of API requests from a single source IP carrying a search engine or crawler User-Agent header but not originating from verified crawler IP ranges.
Repeated failed authentication attempts against the AVideo login API without corresponding rate-limit responses.
Requests to the eight rate-limited AVideo API endpoints where the User-Agent contains substrings such as bot, crawler, or spider.

Detection Strategies

Correlate User-Agent strings with source IP reputation and reverse DNS lookups to identify spoofed crawlers.
Alert on authentication endpoints receiving more than a defined threshold of requests per minute from any single IP, regardless of User-Agent.
Baseline expected crawler traffic patterns and flag deviations, such as bot User-Agents hitting login or password reset endpoints.

Monitoring Recommendations

Enable verbose logging on AVideo API endpoints including client IP, User-Agent, endpoint path, and authentication outcome.
Forward API access logs to a centralized analytics platform for behavioral analysis of authentication traffic.
Monitor for successful logins immediately following bursts of failed attempts from bot-labeled traffic.

How to Mitigate CVE-2026-86186

Immediate Actions Required

Apply the vendor patch referenced in the AVideo GitHub Security Advisory GHSA-qmmw-hmm4-xxp7 as soon as it is available for your deployment.
Force password resets on accounts showing anomalous authentication activity since deployment of the affected version.
Review API access logs for evidence of prior exploitation using bot User-Agent strings against the login endpoint.

Patch Information

Refer to the AVideo GitHub Security Advisory for the fixed version and upgrade instructions. The fix removes the unconditional bot User-Agent exemption from the rate-limit middleware and enforces throttling on all eight protected operations regardless of client-supplied headers.

Workarounds

Deploy a reverse proxy or web application firewall rule that enforces rate limits on the AVideo API login endpoint independently of the application, ignoring the User-Agent header.
Verify bot claims by performing reverse DNS validation of source IPs before granting any crawler exemption at the proxy layer.
Temporarily block or challenge requests advertising crawler User-Agents on authentication endpoints until the patch is applied.

bash

# Example NGINX rate-limit configuration applied to the AVideo login API,
# ignoring User-Agent and keyed only on source IP
limit_req_zone $binary_remote_addr zone=avideo_login:10m rate=5r/m;

server {
    location /api/user/login {
        limit_req zone=avideo_login burst=3 nodelay;
        proxy_pass http://avideo_backend;
    }
}