GHSA-q8x4-x7mp-5vg2 Plug.Cowboy vulnerable to unauthenticated remote DoS via HTTP/2 `:scheme` atom-table exhaustion

• Hex plug_cowboy: >= 2.0.0, < 2.8.1 → fixed in 2.8.1

Summary An unauthenticated remote denial-of-service vulnerability in `Plug.Cowboy.Conn` allows any attacker who can reach an HTTPS Plug.Cowboy listener via HTTP/2 to permanently exhaust the BEAM atom table and crash the entire Erlang VM. Am I Affected? All users running plug_cowboy with HTTP/2 may be affected, this includes Phoenix applications. If another HTTP adapter such as Bandit is used, then the consuming project is not affected. If the HTTP/2 endpoint is exposed directly (without a proxy) then the project will be affected. If a proxy is in use then it depends on the proxy configuration. Many proxies use HTTP/1.1 internally, and would be unaffected. Impact The vulnerability will allow crashing the Erlang VM (BEAM) via atom exhaustion. Mitigation Users are advised to update to plug_cowboy v2.8.1 to mitigate this issue. Credits Plug.Cowboy thanks Peter Ullrich for finding and responsibly disclosing this vulnerability.