CVE-2026-86409

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libcurl AWS SigV4 Authentication State Leak

Publication date: 2026-10-20

Last updated on: 2026-10-29

Assigner: curl

Description

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.

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Meta Information

Published

2026-10-20

Last Modified

2026-10-29

Generated

2026-11-10

AI Q&A

2026-10-21

EPSS Evaluated

2026-11-08

NVD

CVE-2026-86409

EUVD

EUVD-2026-105274

Affected Vendors & Products

Vendor	Product	Version / Range
curl	curl	8.21.0
curl	curl	8.20.0
curl	curl	8.19.0
curl	curl	8.18.0
curl	curl	8.17.0
curl	curl	8.16.0
curl	curl	8.15.0
curl	curl	8.14.1
curl	curl	8.14.0
curl	curl	8.13.0
curl	curl	8.12.1
curl	curl	8.12.0
curl	curl	8.11.1
curl	curl	8.11.0
curl	curl	8.10.1
curl	curl	8.10.0
curl	curl	8.9.1
curl	curl	8.9.0
curl	curl	8.8.0
curl	curl	8.7.1
curl	curl	8.7.0
curl	curl	8.6.0
curl	curl	8.5.0
curl	curl	8.4.0
curl	curl	8.3.0
curl	curl	8.2.1
curl	curl	8.2.0
curl	curl	8.1.2
curl	curl	8.1.1
curl	curl	8.1.0
curl	curl	8.0.1
curl	curl	8.0.0
curl	curl	7.88.1
curl	curl	7.88.0
curl	curl	7.87.0
curl	curl	7.86.0
curl	curl	7.85.0
curl	curl	7.84.0
curl	curl	7.83.1
curl	curl	7.83.0
curl	curl	7.82.0
curl	curl	7.81.0
curl	curl	7.80.0
curl	curl	7.79.1
curl	curl	7.79.0
curl	curl	7.78.0
curl	curl	7.77.0
curl	curl	7.76.1
curl	curl	7.76.0
curl	curl	7.75.0

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 curl's CURLOPT_AWS_SIGV4 option. When set to NULL, it fails to disable AWS SigV4 authentication as expected. Instead, subsequent transfers using the same handle still send an Authorization header with AWS4-HMAC-SHA256, potentially leaking state information like access-key identifiers.

Detection Guidance

Check curl version with 'curl --version' to see if it is between 7.75.0 and 8.21.0. Review application code for use of CURLOPT_AWS_SIGV4 set to NULL. Monitor network traffic for unexpected AWS4-HMAC-SHA256 headers in requests after credential handling.

Impact Analysis

If an application reuses an easy handle and sets CURLOPT_AWS_SIGV4 to NULL before making a request to an attacker-controlled URL, it may unintentionally send a signed SigV4 header. This exposes the access-key identifier and request-bound signature, risking unauthorized access or data leaks. The secret key is not transmitted.

Compliance Impact

This vulnerability could potentially impact compliance with GDPR and HIPAA by exposing AWS access-key identifiers and request-bound signatures through leaked SigV4 headers. Unauthorized data exposure may violate confidentiality requirements under these regulations.

Mitigation Strategies

Upgrade curl to version 8.22.0 or later. If upgrading is not possible, apply the specific patch for your version. Avoid setting CURLOPT_AWS_SIGV4 to NULL in application code. Reuse of easy handles with credentials should be avoided.

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