---
id: "CVE-2026-86409"
kind: "vulnerability"
aliases: ["CVE-2026-86409"]
title: "curl: clearing CURLOPT_AWS_SIGV4 leaves SigV4 auth active on the handle"
severity: "low"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["c", "libcurl", "native-code", "package"]
not_affected_if: ["fresh-handle-per-transfer", "no-aws-sigv4-option"]
published_at: "2026-10-20T20:17:25+00:00"
first_seen_at: "2026-10-23T21:57:21+00:00"
updated_at: "2026-10-25T05:04:39+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-86409", "first_seen_at": "2026-10-23T21:57:21+00:00"}]
---

# curl: clearing CURLOPT_AWS_SIGV4 leaves SigV4 auth active on the handle

Setting CURLOPT_AWS_SIGV4 to NULL does not turn off AWS SigV4 signing, so the next transfer on the same handle still sends an AWS4-HMAC-SHA256 Authorization header. The header goes to whatever URL is requested next, which can leak signing state to an unintended host.

_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-2026-86409

## From the sources

Setting `CURLOPT_AWS_SIGV4` to NULL but does not disable SigV4 authentication,
contrary to expectations and documentation. A subsequent transfer on the same
handle still sends an `Authorization: AWS4-HMAC-SHA256` header to whatever URL
isset next, leaking state information.

---

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