---
id: CVE-2026-87861
title: cross-origin reuse of a Negotiate connection
summary: |-
  When using ambient user credentials, an HTTP request directed to one origin
  may be dispatched over a connection previously authenticated via Negotiate for
  a different origin, leaving the request's intended credentials unused.
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'
cvssSource: adp
cwe:
  - CWE-201
vendor: curl
product: curl
affected:
  - curl >= 8.22.0 <= 8.22.0
  - curl >= 8.21.0 <= 8.21.0
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-10-30T11:54:54.295912Z'
exploitAvailable: true
published: '2026-10-20'
updated: '2026-10-30'
sourceUpdated: '2026-10-30T11:55:20.837Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-87861'
references:
  - url: 'https://curl.se/docs/CVE-2026-87861.json'
    label: json
  - url: 'https://curl.se/docs/CVE-2026-87861.html'
    label: www
  - url: 'https://hackerone.com/reports/3972094'
    label: issue
tags:
  - cve.org
  - exploit-available
epss: 0.00676
epssPercentile: 0.52247
ingestedAt: '2026-10-20T21:19:21.287Z'
---

## Overview

When using ambient user credentials, an HTTP request directed to one origin
may be dispatched over a connection previously authenticated via Negotiate for
a different origin, leaving the request's intended credentials unused.

## Affected

- `curl >= 8.22.0 <= 8.22.0`
- `curl >= 8.21.0 <= 8.21.0`

## Remediation

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