Video Filter YouTube Channel ID Regex Backtracking Triggering 100% CPU Spike
In educational and enterprise environments filtering YouTube content, catastrophic regex backtracking during channel ID extraction drives wad worker processes to 100% CPU, stalling web traffic and triggering conserve mode.
Technical Root Cause Analysis
The FortiOS Video Filter subsystem intercepts streaming video traffic to enforce YouTube Channel ID, Category, and SafeSearch controls. Under proxy inspection, the wad worker inspects HTTP/2 headers and extracts JSON metadata from endpoints such as /youtubei/v1/player and /youtubei/v1/browse.
In FortiOS 7.2.3 through 7.2.6, the pattern matching routine responsible for matching configured channel IDs against the extracted URL parameters utilized a Non-deterministic Finite Automaton (NFA) regex parser with non-anchored greedy wildcards. When clients navigated YouTube playlists with long tracking tokens, dynamic query parameters, or non-matching channel identifiers, the NFA parser suffered catastrophic backtracking (exponential step complexity O(2^n)). Single HTTP requests kept WAD worker threads spinning at 100% CPU utilization for up to 45 seconds, rapidly exhausting all available CPU cores and pushing the system into memory conserve mode.
Affected Firmware & Blast Radius Matrix
| FortiOS Branch | Vulnerable Builds | Confirmed Clean Build | Status & Workaround |
|---|---|---|---|
| FortiOS 7.2 | 7.2.3 – 7.2.6 | 7.2.7+ | Replace regex with exact Channel IDs |
| FortiOS 7.4 | 7.4.0 – 7.4.1 | 7.4.2+ | DFA linear parser integrated |
| FortiOS 7.0 | Low Occurrence | 7.0.12+ | Simplified channel filter syntax |
Platform Impact: School districts, universities, and enterprise branches running FortiOS Video Filtering on proxy-mode policies with YouTube channel whitelist/blacklist policies.
Step 01: Free Verification CLI (Safe Read-Only)
Run these diagnostic commands to determine which WAD worker processes are saturated at 100% CPU and inspect video filter status:
Diagnostic Commands
# 1. Check top CPU-consuming WAD worker processes in real-time
diagnose sys top 2 5 | grep wad
# 2. Inspect active WAD worker threads and connection statistics
diagnose test application wad 1000
# 3. View active video filter configuration and channel rules
show videofilter youtube-key
show videofilter profileRemediation & Workaround Steps (Teaser Preview)
Relieve 100% CPU spikes immediately without dropping web browsing across the network:
Frequently Asked Questions
Catastrophic backtracking occurs when an NFA regular expression engine evaluates ambiguous nested repetitions (such as '(.*[a-zA-Z0-9]+)+') against long or non-matching URI query strings. In FortiOS 7.2.3–7.2.6, parsing modern YouTube API payloads with complex channel slugs caused exponential execution paths, locking WAD CPU cores at 100%.
K-12 schools heavily enforce YouTube channel restrictions under CIPA compliance guidelines, maintaining whitelists of hundreds of educational channels while blocking entertainment videos. High concurrent student browsing triggers thousands of simultaneous channel ID regex evaluations.
Yes. Removing the video-filter profile from active firewall policies leaves Web Filtering, Antivirus, and SSL inspection intact while immediately releasing saturated CPU cores.