Vulnerability · Published May 13, 2026 · Assigned by curl
CVE-2026-6276stale custom cookie host causes cookie leak
High 7.5
In plain English
A high-severity security flaw in curl from curl. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.3%top 77.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.21 | curl | 8.14.1-r3 | ALPINE-CVE-2026-6276 |
| Alpine:v3.22 | curl | 8.14.1-r4 | ALPINE-CVE-2026-6276 |
| Alpine:v3.23 | curl | 8.20.0-r0 | ALPINE-CVE-2026-6276 |
| Alpine:v3.24 | curl | 8.20.0-r0 | ALPINE-CVE-2026-6276 |
| Debian:12 | curl | no fix listed | DEBIAN-CVE-2026-6276 |
| Debian:13 | curl | 8.14.1-2+deb13u4 | DEBIAN-CVE-2026-6276 |
| Debian:14 | curl | 8.20.0~rc3-1 | DEBIAN-CVE-2026-6276 |
| Ubuntu:22.04:LTS | curl | 7.81.0-1ubuntu1.24 | UBUNTU-CVE-2026-6276 |
| Ubuntu:24.04:LTS | curl | 8.5.0-2ubuntu10.9 | UBUNTU-CVE-2026-6276 |
| Ubuntu:25.10 | curl | 8.14.1-2ubuntu1.3 | UBUNTU-CVE-2026-6276 |
| Ubuntu:26.04:LTS | curl | 8.18.0-1ubuntu2.1 | UBUNTU-CVE-2026-6276 |
Affected products (as reported)
Weakness: CWE-346 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H