Description
A flaw was found in curl. When an application attempts to disable Amazon Web Services Signature Version 4 (AWS SigV4) authentication on a reused connection handle, curl fails to clear the setting as expected. If the application subsequently directs a request to an untrusted or attacker-controlled server using the same handle, curl unintentionally transmits the signed authorization header. This flaw allows a remote attacker to obtain access key identifiers and request signatures, leading to information disclosure.
Published: 2026-10-20
Score: 5.3 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Ubuntu USN Ubuntu USN USN-8927-1 curl vulnerabilities
Ubuntu USN Ubuntu USN USN-8932-1 curl vulnerabilities
Ubuntu USN Ubuntu USN USN-8927-2 curl vulnerabilities
History

Tue, 20 Oct 2026 20:00:00 +0000

Type Values Removed Values Added
Description A flaw was found in curl. When an application attempts to disable Amazon Web Services Signature Version 4 (AWS SigV4) authentication on a reused connection handle, curl fails to clear the setting as expected. If the application subsequently directs a request to an untrusted or attacker-controlled server using the same handle, curl unintentionally transmits the signed authorization header. This flaw allows a remote attacker to obtain access key identifiers and request signatures, leading to information disclosure. 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.
Title curl: curl: stale SigV4 headers sent unintended stale SigV4 headers sent unintended
References

Sun, 18 Oct 2026 14:30:00 +0000

Type Values Removed Values Added
First Time appeared Curl
Curl curl
Vendors & Products Curl
Curl curl

Sat, 17 Oct 2026 00:30:00 +0000

Type Values Removed Values Added
Description A flaw was found in curl. When an application attempts to disable Amazon Web Services Signature Version 4 (AWS SigV4) authentication on a reused connection handle, curl fails to clear the setting as expected. If the application subsequently directs a request to an untrusted or attacker-controlled server using the same handle, curl unintentionally transmits the signed authorization header. This flaw allows a remote attacker to obtain access key identifiers and request signatures, leading to information disclosure.
Title curl: curl: stale SigV4 headers sent unintended
Weaknesses CWE-201
References
Metrics threat_severity

None

 cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N'}

threat_severity

Low

Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: curl

Published:

Updated: 2026-10-20T19:57:01.794Z

Reserved: 2026-09-07T12:11:44.926Z

Link: CVE-2026-86409

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-20T20:17:25.223

Modified: 2026-10-20T20:17:25.223

Link: CVE-2026-86409

cve-icon Redhat

Severity : Low

Publid Date: 2026-10-14T12:00:00Z

Links: CVE-2026-86409 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-18T14:15:14Z

Weaknesses
  • CWE-201

    Insertion of Sensitive Information Into Sent Data