CVE-2026-86409

stale SigV4 headers sent unintended

View on CVE.org
Published Oct 20, 2026 CVSS 3.1 · 8.1 High EPSS 1.1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

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
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

 ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}
Type Values Removed Values Added
Metrics 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'}

 cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}
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
Type Values Removed Values Added
First Time appeared Curl
Curl curl
Vendors & Products Curl
Curl curl
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
Earlier changes (1)
Weaknesses

Sources

Status
PUBLISHED
Assigner
curl
Published
Updated
Oct 29, 2026, 6:33 PM
Reserved
Sep 7, 2026, 12:11 PM

View source JSON

Updated
Oct 29, 2026, 6:31 PM

JSON

Status
Awaiting Analysis
Published
Oct 20, 2026, 8:17 PM
Modified
Oct 29, 2026, 7:17 PM

View source JSON

Severity
Low
Public date
Oct 14, 2026, 12:00 PM

View source Bugzilla JSON

Updated
Oct 29, 2026, 9:30 PM

JSON