What’s Vulnerable › Vulnerabilities

CVE-2026-6276: stale custom cookie host causes cookie leak

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-05-13 · updated 2026-09-15
• Weakness: CWE-346

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.

Affected products

• curl: from 7.71.0 before 8.20.0 — fixed in 8.20.0

How to fix

Upgrade to a fixed version: curl 8.20.0. Check the vendor advisory for mitigations.

References

• https://curl.se/docs/CVE-2026-6276.html
• https://curl.se/docs/CVE-2026-6276.json
• https://hackerone.com/reports/3671818
• http://www.openwall.com/lists/oss-security/2026/04/29/13
• https://hackerone.com/reports/3671818

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