yt-dlp-web-ui CVE-2026-109966

No special conditions - remote unauthenticated exploitation against default configurations of yt-dlp-web-ui ≤4.0.0, requiring only network reachability to the JSON-RPC endpoints /rpc/http or /rpc/ws and invocation of the Service.Formats method with a dash-prefixed url parameter. The only limiting factors are that the instance must be network-reachable to the attacker (self-hosted tools are often bound to LAN/localhost or behind a reverse proxy rather than internet-exposed) and that meaningful disclosure is constrained to files yt-dlp can parse as info-JSON and reflect back, so arbitrary binary or non-JSON files are not cleanly exfiltrated. No authentication, user interaction, or non-default setting is needed.

This is a medium-severity information-disclosure flaw whose signals are internally consistent rather than conflicting. The vendor-supplied CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N) describes network-reachable, low-complexity, unauthenticated exploitation with no user interaction - matching the description's claim of unauthenticated remote attackers hitting the /rpc/http and /rpc/ws JSON-RPC endpoints. Impact is deliberately scoped low: VC:L with VI:N/VA:N, reflecting that the attacker can read attacker-chosen JSON files from the server filesystem but cannot modify data or affect availability, and disclosure is constrained to content yt-dlp will parse as info-JSON and reflect back. Publicly available exploit code exists (VulnCheck advisory plus a third-party write-up with POC), which raises practical exploitability, but the issue is NOT in CISA KEV and no EPSS score was provided, so there is no evidence of active or widespread exploitation - treat this as a disclosed, POC-backed bug rather than a confirmed in-the-wild campaign. Net: a genuine priority for anyone exposing yt-dlp-web-ui to untrusted networks (trivial to exploit, no auth), but the low confidentiality-only impact and niche deployment footprint keep it below critical-patch-now urgency. No key signals conflict; the main missing datum is EPSS probability.

An attacker who can reach a yt-dlp-web-ui instance (≤4.0.0) sends a Service.Formats JSON-RPC call to /rpc/http or /rpc/ws with a dash-prefixed url value such as '--load-info-json=/path/to/file', causing yt-dlp to load an attacker-specified JSON file from the server filesystem and reflect its contents in the response. A public POC and VulnCheck advisory demonstrate the argument-injection technique, so exploitation requires no novel research. Because the endpoint is unauthenticated, any network-adjacent or internet-exposed instance is reachable without credentials.