EEF-CVE-2026-47066

Infinite loop in Alt-Svc header parser in hackney

## Summary Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in benoitc hackney allows Excessive Allocation. The Alt-Svc response header parser in src/hackney\_altsvc.erl does not guarantee forward progress. When parse\_token/2 receives a non-token, non-whitespace, non-comma byte (e.g. !, @, =, ;), it returns the input unchanged. skip\_comma/1 also returns the buffer unchanged when the first byte is not a comma. parse\_entries/2 then recurses with identical data, creating a tight infinite tail-recursive loop that pins a scheduler at 100% CPU. The calling process never returns. The entry point parse\_and\_cache/3 is called synchronously in the connection process on every HTTP response. A single-byte Alt-Svc: ! response header is sufficient to trigger the hang; the header is fully controlled by any HTTP origin the client connects to. This issue affects hackney: from 2.0.0-beta.1 before 4.0.1.