CVE-2026-86415

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libcurl Schannel Connection Cache Authentication Bypass

Publication date: 2026-10-20

Last updated on: 2026-10-30

Assigner: curl

Description

libcurl's connection cache match function never considers the automatic client certificate option, so a cached, already authenticated Schannel connection can be handed to a transfer that got redirected to a different origin, even though the code explicitly switched off the auto client cert option for that transfer to prevent exactly this.

CVSS Scores

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Meta Information

Published

2026-10-20

Last Modified

2026-10-30

Generated

2026-11-10

AI Q&A

2026-10-21

EPSS Evaluated

2026-11-08

NVD

CVE-2026-86415

Affected Vendors & Products

Vendor	Product	Version / Range
curl	curl	8.22.0
curl	curl	8.21.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-201	The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor.

Attack-Flow Graph

Executive Summary

This vulnerability involves libcurl's connection cache not checking the automatic client certificate option. A cached Schannel connection that was already authenticated might be reused for a transfer redirected to a different origin, even when the transfer explicitly disabled the auto client certificate option to prevent this exact issue.

Detection Guidance

This vulnerability involves libcurl's connection cache not respecting the automatic client certificate option during transfers. Detection requires checking if libcurl versions affected by this issue are installed and monitoring for unexpected certificate usage during transfers.

Impact Analysis

This could allow unauthorized access to sensitive data if a connection is reused for a different origin than intended. It may lead to data leaks or security breaches by bypassing intended authentication restrictions.

Compliance Impact

This vulnerability could violate compliance requirements that mandate strict access controls and data protection, such as GDPR's data security principles or HIPAA's safeguards for protected health information, by enabling unauthorized data access.

Mitigation Strategies

Update libcurl to the latest patched version to address the connection cache issue with Schannel authentication.

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