stale custom cookie host causes cookie leak
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.
02 / AFFECTED SOFTWARE
Affected packages
62 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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.
05 / REFERENCES
Further evidence
- http://www.openwall.com/lists/oss-security/2026/04/29/13
- https://curl.se/docs/CVE-2026-6276.html
- https://curl.se/docs/CVE-2026-6276.json
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6276.json
- https://hackerone.com/reports/3671818
- https://nvd.nist.gov/vuln/detail/CVE-2026-6276