Description
Using libcurl, when a custom `Host:` header is first set for an HTTP request
and a second request is subsequently done using the same *easy handle* but
without the custom `Host:` header set, the second request would use stale
information and pass on cookies meant for the first host in the second
request. Leak them.
Published: 2026-05-13
Score: 7.5 High
EPSS: < 1% Very Low
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-8227-1 curl vulnerabilities
History

Thu, 14 May 2026 14:30:00 +0000

Type Values Removed Values Added
First Time appeared Haxx
Haxx curl
Weaknesses CWE-319
CPEs cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:*
Vendors & Products Haxx
Haxx curl

Wed, 13 May 2026 18:30:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N'}

 ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Wed, 13 May 2026 15:30:00 +0000

Type Values Removed Values Added
References

Wed, 13 May 2026 09:15:00 +0000

Type Values Removed Values Added
Description A flaw was found in libcurl. This vulnerability allows for information disclosure when a custom `Host:` header is used in an initial HTTP request, and a subsequent request reuses the same connection without specifying a new `Host:` header. This can lead to libcurl incorrectly sending cookies intended for the first host to the second host, resulting in a cookie leak. This issue is categorized as an Origin Validation Error (CWE-346). Exploitation typically requires specific debugging configurations. Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.
Title curl: libcurl: Information disclosure due to cookie leak when reusing connections with custom Host headers stale custom cookie host causes cookie leak
References

Fri, 01 May 2026 01:45:00 +0000

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

Fri, 01 May 2026 00:15:00 +0000

Type Values Removed Values Added
Description A flaw was found in libcurl. This vulnerability allows for information disclosure when a custom `Host:` header is used in an initial HTTP request, and a subsequent request reuses the same connection without specifying a new `Host:` header. This can lead to libcurl incorrectly sending cookies intended for the first host to the second host, resulting in a cookie leak. This issue is categorized as an Origin Validation Error (CWE-346). Exploitation typically requires specific debugging configurations.
Title curl: libcurl: Information disclosure due to cookie leak when reusing connections with custom Host headers
Weaknesses CWE-346
References
Metrics threat_severity

None

 cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N'}

threat_severity

Low

Subscriptions

Curl Libcurl
Haxx Curl
cve-icon MITRE

Status: PUBLISHED

Assigner: curl

Published:

Updated: 2026-05-13T17:26:06.894Z

Reserved: 2026-04-14T14:01:54.772Z

Link: CVE-2026-6276

cve-icon Vulnrichment

Updated: 2026-05-13T09:05:37.539Z

cve-icon NVD

Status : Analyzed

Published: 2026-05-13T13:01:56.800

Modified: 2026-05-14T14:21:06.997

Link: CVE-2026-6276

cve-icon Redhat

Severity : Low

Publid Date: 2026-04-29T00:00:00Z

Links: CVE-2026-6276 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-05-14T15:30:16Z

Weaknesses