CVE-2026-47066

Description

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.

PUBLISHED Reserved 2026-05-18 | Published 2026-05-25 | Updated 2026-05-27 | Assigner EEF

Problem types

CWE-835 Loop with Unreachable Exit Condition ('Infinite Loop')

Product status

Credits

Peter Ullrich finder

Benoit Chesneau remediation developer

Jonatan Männchen / EEF analyst

References

github.com/...ackney/security/advisories/GHSA-6cp8-v795-jr2j exploit

github.com/...ackney/security/advisories/GHSA-6cp8-v795-jr2j vendor-advisory related

cna.erlef.org/cves/CVE-2026-47066.html related

osv.dev/vulnerability/EEF-CVE-2026-47066 related

github.com/...ommit/e548aba1f97ffa3f4750da7b772998fb78c01894 patch

cve.org (CVE-2026-47066)

nvd.nist.gov (CVE-2026-47066)

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