Weakness Type (CWE)

CWE-436 — CWE-436 Interpretation Conflict

CAPEC

CVSS 4.0 Score

6.9

MEDIUM

CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N

Vulnerability 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.

Affected

pkg:hex/hackney

Module Source File Routine
hackney_url src/hackney_url.erl hackney_url:normalize/2
Status Type Version Changes / Fixed in
affected semver ⓘ 0.13.0 < 4.0.1

pkg:github/benoitc/hackney

Module Source File Routine
hackney_url src/hackney_url.erl hackney_url:normalize/2
Status Type Version Changes / Fixed in
affected git ⓘ 4d72550758 < 452620a92e

References

Credits

  • Finder: Ganbagana
  • Remediation developer: Benoit Chesneau
  • Analyst: Jonatan Männchen

CVE record as JSON:  GET /cves/CVE-2026-47076.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-47076.json