Which versions of hackney are affected by CVE-2026-47066?

Benoitc's hackney Erlang HTTP client (versions 2.0.0-beta.1 through 4.0.0) contains a denial-of-service vulnerability triggered by malformed HTTP response headers from remote servers, which could…. A patch is available.

Is there a public PoC exploit available for CVE-2026-47066?

Yes, a public proof-of-concept exploit is available for CVE-2026-47066. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2026-47066?

Within 24 hours: Complete inventory of all systems running benoitc's hackney versions 2.0.0-beta.1 through 4.0.0, prioritizing production services and those communicating with external HTTP sources. Within 7 days: Upgrade all affected hackney installations to version 4.0.1 or later. Within 30 days: Verify complete removal of vulnerable versions through dependency scanning and confirm no deprecated instances remain in development, staging, or production environments.

hackney CVE-2026-47066

Q: What is the CVSS score of CVE-2026-47066?

CVE-2026-47066 has a CVSS 4.0 base score of 8.7 (High). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.0%.

EUVD-2026-31686 HIGH

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

2026-05-25 EEF

GHSA-6cp8-v795-jr2j

Denial Of Service Hackney

8.7

CVSS 4.0 · NVD

Severity by source

NVD PRIMARY

8.7 HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Source Code Evidence Fetched

Jun 08, 2026 - 09:57 vuln.today

Analysis Generated

Jun 08, 2026 - 09:57 vuln.today

CVSS changed

May 26, 2026 - 17:22 NVD

8.7 (HIGH)

CVE Published

May 25, 2026 - 14:00 nvd

UNKNOWN (no severity yet)

DescriptionCVE.org

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.

AnalysisAI

Denial-of-service in benoitc's hackney Erlang HTTP client (versions 2.0.0-beta.1 through 4.0.0) allows any HTTP origin server to pin a client process at 100% CPU by returning a malformed Alt-Svc response header. The flaw is a CWE-835 infinite loop in the Alt-Svc parser, triggerable by a single byte such as '!' in the header value. No public exploit identified at time of analysis, EPSS is low (0.04%), but SSVC rates exploitation as POC and the attack is automatable; a vendor patch is available in 4.0.1.

Technical ContextAI

hackney is a widely embedded Erlang HTTP client library (e.g., used transitively by HTTPoison and many Elixir/Erlang services). The vulnerable code is src/hackney_altsvc.erl, which parses RFC 7838 Alt-Svc response headers. parse_token/2 returns the buffer unchanged when it encounters a non-token, non-whitespace, non-comma byte, and skip_comma/1 likewise returns the buffer unchanged when the leading byte is not a comma. parse_entries/2 then tail-recurses on identical input, never making forward progress - a textbook CWE-835 'Loop with Unreachable Exit Condition'. Because parse_and_cache/3 runs synchronously inside the connection process on every HTTP response, the offending Erlang scheduler thread is starved indefinitely. The fix (commit e548aba) introduces seek_next_entry/1 to advance past a malformed lead byte until the next comma, guaranteeing progress.

RemediationAI

Vendor-released patch: upgrade hackney to 4.0.1 or later, which adds the seek_next_entry/1 forward-progress guard in src/hackney_altsvc.erl (commit https://github.com/benoitc/hackney/commit/e548aba1f97ffa3f4750da7b772998fb78c01894); see the advisory at https://github.com/benoitc/hackney/security/advisories/GHSA-6cp8-v795-jr2j. For Elixir/Erlang projects, bump the direct or transitive hackney dependency in mix.exs / rebar.config and rebuild. If you cannot upgrade immediately, compensating controls are limited because Alt-Svc is sent by the server: restrict hackney to a known allowlist of trusted origins and disallow user-controlled URLs (mitigates SSRF-style abuse but breaks general-purpose client use), terminate outbound HTTP traffic through a forward proxy that strips the Alt-Svc response header (loses any legitimate HTTP/3 upgrade hints), or wrap hackney calls in a supervised, time-bounded task so a stalled scheduler can be killed (still wastes CPU until the timer fires and does not prevent repeated triggering).