---
id: "CVE-2026-86414"
kind: "vulnerability"
aliases: ["CVE-2026-86414"]
title: "libcurl: malicious proxy can harvest origin credentials via CONNECT 401"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["c", "kerberos", "libcurl", "package", "proxy"]
not_affected_if: ["no-origin-credentials", "no-proxy"]
published_at: "2026-10-20T21:17:19+00:00"
first_seen_at: "2026-10-23T21:57:21+00:00"
updated_at: "2026-10-25T05:04:31+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-86414", "first_seen_at": "2026-10-23T21:57:21+00:00"}]
---

# libcurl: malicious proxy can harvest origin credentials via CONNECT 401

A malicious HTTP proxy can answer a CONNECT tunnel request with a 401 WWW-Authenticate challenge instead of 407, which tricks libcurl into sending the origin server's credentials to the proxy. An attacker running or controlling a proxy can capture Basic passwords or Negotiate/Kerberos tickets meant for the origin.

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

## How to check

- unknown

## Fix

- unknown

## Timeline

- 2026-10-23T21:57:21+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-86414

## From the sources

An HTTP proxy can trick libcurl into sending the origin's credentials (Basic
password, or a Negotiate/Kerberos ticket) to the proxy itself, by answering
the `CONNECT` tunnel request with 401 `WWW-Authenticate:` instead of the
expected 407 `Proxy-Authenticate:`.

---

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