CVE-2026-47066
HighPublic exploitInfinite loop in Alt-Svc header parser in hackney
Published May 25, 2026 · Updated Oct 8, 2026 · Also known as EEF-CVE-2026-47066, EUVD-2026-31686, GHSA-6cp8-v795-jr2j
Key Facts
Patch immediately- CVE-2026-47066 is a high-severity vulnerability (CVSS 8.7 v4) affecting Hackney (Benoitc).
- It is not listed in any known-exploited vulnerabilities catalog. Public exploit code is available.
- EPSS estimates a 0.7% probability of exploitation in the next 30 days.
- Fixed versions are available, including Hackney 4.0.1, Hackney e548aba1f97ffa3f4750da7b772998fb78c01894.
- Brandefense priority: patch immediately, because public exploit code exists for a high-severity flaw.
CVSS v4
8.7
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 (30-day exploit likelihood)
0.7%
Exploited in the wild
No known
Not in a known-exploited catalog
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2026-47066 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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.
Affected Products
3 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| HackneyBenoitc | >= 2.0.0-beta.1 | 4.0.1 |
Patched Releases
Hackney
4.0.1, e548aba1f97ffa3f4750da7b772998fb78c01894
Timeline
Publicly disclosed
May 25, 2026
Last updated
Oct 8, 2026
Weakness Type
- CWE-835 Loop with Unreachable Exit Condition ('Infinite Loop')
References
- advisoryGHSA advisory
- advisoryhttps://github.com/benoitc/hackney/security/advisories/GHSA-6cp8-v795-jr2j
- advisoryhttps://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47066.json
- advisoryhttps://nvd.nist.gov/vuln/detail/CVE-2026-47066
- patchhttps://github.com/benoitc/hackney/commit/e548aba1f97ffa3f4750da7b772998fb78c01894
FAQ
Common Questions.
Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in benoitc hackney allows Excessive Allocation.
Affected: Hackney (Benoitc) versions >= 2.0.0-beta.1. The full list is in the CVE brief.
It is not listed in any known-exploited vulnerabilities catalog.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
Public exploit code is available.
Fixed versions are available, including Hackney 4.0.1, Hackney e548aba1f97ffa3f4750da7b772998fb78c01894.
Brandefense priority: patch immediately, because public exploit code exists for a high-severity flaw.
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