CVE-2026-6276

stale custom cookie host causes cookie leak

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Published May 13, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8227-1 curl vulnerabilities
History
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
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'}
Type Values Removed Values Added
References
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
Type Values Removed Values Added
First Time appeared Curl
Curl libcurl
Vendors & Products Curl
Curl libcurl
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
Earlier changes (1)
Weaknesses

Sources

Status
PUBLISHED
Assigner
curl
Published
Updated
Sep 15, 2026, 6:03 AM
Reserved
Apr 14, 2026, 2:01 PM

View source JSON

Updated
May 13, 2026, 9:05 AM

JSON

Status
Modified
Published
May 13, 2026, 1:01 PM
Modified
Nov 11, 2026, 8:10 PM

View source JSON

Severity
Low
Public date
Apr 29, 2026, 12:00 AM

View source Bugzilla JSON

Updated
May 14, 2026, 3:30 PM

JSON