---
id: "CVE-2026-115700"
kind: "vulnerability"
aliases: ["CVE-2026-115700"]
title: "Erlang hackney: encoded IP literals bypass SSRF allowlists in URL parsing"
severity: "medium"
cvss: 6.9
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["elixir", "erlang", "hackney", "package", "self-hosted"]
not_affected_if: ["fixed-destination-hosts", "hackney-below-4.0.1-or-4.9.0-plus", "no-user-supplied-urls"]
published_at: "2026-10-26T14:16:32+00:00"
first_seen_at: "2026-10-26T14:30:36+00:00"
updated_at: "2026-10-26T14:32:34+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-115700", "first_seen_at": "2026-10-26T14:30:36+00:00"}]
---

# Erlang hackney: encoded IP literals bypass SSRF allowlists in URL parsing

hackney, an Erlang HTTP client, connects to IP addresses written in forms that an application's allowlist does not recognize, such as a percent-encoded bracketed IPv6 literal or an IPv4 address with a trailing dot. An attacker who can supply a URL or a redirect target can therefore reach internal addresses such as 127.0.0.1 and make server-side requests there.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the hackney version in the project lock file (rebar.lock or the mix.lock/rebar config) for `hackney` versions from `4.0.1` up to but not including `4.9.0`
- Search application code for calls to `uri_string:parse/1` or `inet:parse_address/1` used as an SSRF allowlist on URLs passed to hackney
- unknown whether the sources list any further detection step

## Fix

- Upgrade hackney to `4.9.0` or later
- Until upgraded, validate the resolved address of the final connection target rather than the raw URL host, and reject redirects to untrusted hosts

## Timeline

- 2026-10-26T14:30:36+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-115700

## From the sources

Interpretation Conflict vulnerability in hackney_url in benoitc hackney allows Server Side Request Forgery via a percent-encoded bracketed IPv6 literal or an IP literal with a trailing dot. A host such as %5B%3A%3Affff%3A127%2E0%2E0%2E1%5D (decoding to [::ffff:127.0.0.1]) or 127.0.0.1. is not an IP address to a caller's allowlist built on uri_string:parse/1 and inet:parse_address/1, while hackney connects to the address it denotes. The same applies to a Location target when redirects are followed.

The IP-literal gate that hackney_url:normalize/2 applies to a percent-decoded host, added to close the percent-encoded IP bypass of CVE-2026-47076, passes the decoded value to inet_parse:address/1 as is. The connect path in hackney_happy:parse_address/1 drops a surrounding bracket pair, and the resolver ignores a trailing dot, so both forms pass the gate and still reach the literal address. Domain names with a trailing dot and unencoded IPv6 literals are not affected.

This issue affects hackney: from 4.0.1 before 4.9.0.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_