Interpretation Conflict vulnerability in benoitc hackney allows Server Side Request Forgery. hackney_url:normalize/2 URL-decodes the host component after the URL has been parsed into a #hackney_url{} record. OTP's uri_string:parse/1 and inet:parse_address/1 do not decode percent-escapes in the host, so a URL such as http://%31%32%37%2E%30%2E%30%2E%31/ is seen by a caller's allowlist validator with host %31%32%37%2E%30%2E%30%2E%31 (not an IP address), which passes the allowlist check. hackney's normalizer then decodes the host to 127.0.0.1 and opens a TCP connection to loopback. Because hackney:request/5 always calls hackney_url:normalize/2 with no opt-out, every request that takes a binary or list URL is affected. The same technique reaches cloud instance metadata services (169.254.169.254), RFC1918 networks, and any admin interface listening on localhost.
This issue affects hackney: from 0.13.0 before 4.0.1.
This issue affects hackney: from 0.13.0 before 4.0.1.
Advisories
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Fixes
Solution
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Workaround
No workaround given by the vendor.
References
History
Mon, 25 May 2026 14:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | Interpretation Conflict vulnerability in benoitc hackney allows Server Side Request Forgery. hackney_url:normalize/2 URL-decodes the host component after the URL has been parsed into a #hackney_url{} record. OTP's uri_string:parse/1 and inet:parse_address/1 do not decode percent-escapes in the host, so a URL such as http://%31%32%37%2E%30%2E%30%2E%31/ is seen by a caller's allowlist validator with host %31%32%37%2E%30%2E%30%2E%31 (not an IP address), which passes the allowlist check. hackney's normalizer then decodes the host to 127.0.0.1 and opens a TCP connection to loopback. Because hackney:request/5 always calls hackney_url:normalize/2 with no opt-out, every request that takes a binary or list URL is affected. The same technique reaches cloud instance metadata services (169.254.169.254), RFC1918 networks, and any admin interface listening on localhost. This issue affects hackney: from 0.13.0 before 4.0.1. | |
| Title | SSRF allowlist bypass via percent-encoded host in hackney | |
| First Time appeared |
Benoitc
Benoitc hackney |
|
| Weaknesses | CWE-436 CWE-918 |
|
| CPEs | cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Benoitc
Benoitc hackney |
|
| References |
| |
| Metrics |
cvssV4_0
|
Projects
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Status: PUBLISHED
Assigner: EEF
Published:
Updated: 2026-05-25T14:00:46.707Z
Reserved: 2026-05-18T17:28:10.319Z
Link: CVE-2026-47076
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OpenCVE Enrichment
Updated: 2026-05-25T15:45:16Z