---
id: CVE-2026-115693
title: Custom cacerts or cacertfile do not restrict trust to the pinned CA in hackney
summary: >-
  Improper Certificate Validation vulnerability in hackney_ssl in benoitc
  hackney allows an on-path attacker to impersonate a server pinned to a private
  certificate authority via a certificate chain that ends in a publicly trusted
  root. ha…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N'
cvssSource: cna
cwe:
  - CWE-295
vendor: benoitc
product: hackney
affected:
  - hackney >= 1.24.0 < 4.9.0
  - >-
    benoitc/hackney >= d8a9afcf5c3849904274e2eba1df56c63d1a1a0c <
    915eb5737e9c489d8fc22eec8cdae30e9b027be4
published: '2026-10-26'
updated: '2026-10-26'
sourceUpdated: '2026-10-26T13:49:29.374Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-115693'
references:
  - url: 'https://github.com/benoitc/hackney/pull/978'
    label: >-
      Drop the certifi partial_chain when the caller pins cacerts or cacertfile
      (benoitc/hackney#978)
  - url: 'https://cna.erlef.org/cves/CVE-2026-115693.html'
    label: EEF CNA record for CVE-2026-115693
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-115693'
    label: OSV record EEF-CVE-2026-115693
  - url: 'https://github.com/benoitc/hackney/releases/tag/4.9.0'
    label: hackney 4.9.0 release notes
  - url: >-
      https://github.com/benoitc/hackney/commit/d8a9afcf5c3849904274e2eba1df56c63d1a1a0c
    label: Introducing commit d8a9afc in benoitc/hackney
  - url: >-
      https://github.com/benoitc/hackney/commit/915eb5737e9c489d8fc22eec8cdae30e9b027be4
    label: Fix commit 915eb57 in benoitc/hackney
tags:
  - cve.org
ingestedAt: '2026-10-26T14:27:31.815Z'
---

## Overview

Improper Certificate Validation vulnerability in hackney_ssl in benoitc hackney allows an on-path attacker to impersonate a server pinned to a private certificate authority via a certificate chain that ends in a publicly trusted root. hackney adds {partial_chain, fun hackney_ssl:partial_chain/1} to every verify_peer configuration. The callback returns any certificate in the peer chain whose public key matches a root in the bundled certifi store as the trust anchor, and OTP honours that callback over the configured cacerts. hackney_ssl:merge_ssl_opts/3 kept the callback when the caller replaced the trust store with cacerts or cacertfile in ssl_options, so a connection pinned to a private CA still accepted any chain that carried a publicly trusted root.

The hostname check still applies, so the attacker needs a publicly trusted certificate for the pinned hostname.

This issue affects hackney: from 1.24.0 before 4.9.0.

## Affected

- `hackney >= 1.24.0 < 4.9.0`
- `benoitc/hackney >= d8a9afcf5c3849904274e2eba1df56c63d1a1a0c < 915eb5737e9c489d8fc22eec8cdae30e9b027be4`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

### Workarounds

Pass your own {partial_chain, Fun} in ssl_options alongside cacerts or cacertfile. A caller-supplied partial_chain replaces hackney's in the merge, and a callback that returns unknown_ca makes OTP validate against the configured cacerts only.