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

CVE-2026-6276 is fixed in 7 products on 1 platform, first by curl 8.18.0-1ubuntu2.1, released April 29, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-6276
- Priority: High
- CVSS: 7.5 (Moderate)
- EPSS: 0.0030
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 29, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-6276

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | curl Debian 13.5 (trixie) | 8.14.1-2+deb13u4 | [DEBIAN-CVE-2026-6276](https://patchblox.com/security/data/fix/linux/debian-cve-2026-6276.md) | May 15, 2026 |
| Linux | curl Debian 14 | 8.20.0~rc3-1 | [DEBIAN-CVE-2026-6276](https://patchblox.com/security/data/fix/linux/debian-cve-2026-6276.md) | May 15, 2026 |
| Linux | curl Ubuntu 22.04.1 LTS (jammy) | 7.81.0-1ubuntu1.24 | [curl 7.81.0-1ubuntu1.24](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-curl-7.81.0-1ubuntu1.24.md) | May 15, 2026 |
| Linux | curl Ubuntu 24.04.5 LTS (noble) | 8.5.0-2ubuntu10.9 | [curl 8.5.0-2ubuntu10.9](https://patchblox.com/security/data/fix/linux/ubuntu-noble-curl-8.5.0-2ubuntu10.9.md) | May 15, 2026 |
| Linux | curl Ubuntu 25.10 (questing) | 8.14.1-2ubuntu1.3 | [curl 8.14.1-2ubuntu1.3](https://patchblox.com/security/data/fix/linux/ubuntu-questing-curl-8.14.1-2ubuntu1.3.md) | May 15, 2026 |
| Linux | curl Ubuntu 26.04.1 LTS (resolute) | 8.18.0-1ubuntu2.1 | [curl 8.18.0-1ubuntu2.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-curl-8.18.0-1ubuntu2.1.md) | Apr 29, 2026 |
| Linux | curl opensuse-leap 16.0 | 8.14.1-160000.6.1 | [OPENSUSE-SU-2026:20973-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-20973-1.md) | Jun 17, 2026 |
| Linux | curl sles 15.7 | 8.14.1-150700.7.23.1 | [SUSE-SU-2026:3798-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3798-1.md) | Aug 25, 2026 |
| Linux | curl sles 16.0 | 8.14.1-160000.6.1 | [SUSE-SU-2026:22156-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22156-1.md) | Jun 17, 2026 |
| Linux | curl-mini sles 16.0 | 8.14.1-160000.6.1 | [SUSE-SU-2026:22156-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22156-1.md) | Jun 17, 2026 |
| Linux | libcurl3-gnutls Ubuntu 22.04.1 LTS (jammy) | 7.81.0-1ubuntu1.24 | [libcurl3-gnutls 7.81.0-1ubuntu1.24](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libcurl3-gnutls-7.81.0-1ubuntu1.24.md) | May 15, 2026 |
| Linux | libcurl3-nss Ubuntu 22.04.1 LTS (jammy) | 7.81.0-1ubuntu1.24 | [libcurl3-nss 7.81.0-1ubuntu1.24](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libcurl3-nss-7.81.0-1ubuntu1.24.md) | May 15, 2026 |
| Linux | libcurl3t64-gnutls Ubuntu 24.04.5 LTS (noble) | 8.5.0-2ubuntu10.9 | [libcurl3t64-gnutls 8.5.0-2ubuntu10.9](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libcurl3t64-gnutls-8.5.0-2ubuntu10.9.md) | May 15, 2026 |
| Linux | libcurl3t64-gnutls Ubuntu 25.10 (questing) | 8.14.1-2ubuntu1.3 | [libcurl3t64-gnutls 8.14.1-2ubuntu1.3](https://patchblox.com/security/data/fix/linux/ubuntu-questing-libcurl3t64-gnutls-8.14.1-2ubuntu1.3.md) | May 15, 2026 |
| Linux | libcurl3t64-gnutls Ubuntu 26.04.1 LTS (resolute) | 8.18.0-1ubuntu2.1 | [libcurl3t64-gnutls 8.18.0-1ubuntu2.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libcurl3t64-gnutls-8.18.0-1ubuntu2.1.md) | Apr 29, 2026 |
| Linux | libcurl4 Ubuntu 22.04.1 LTS (jammy) | 7.81.0-1ubuntu1.24 | [libcurl4 7.81.0-1ubuntu1.24](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libcurl4-7.81.0-1ubuntu1.24.md) | May 15, 2026 |
| Linux | libcurl4t64 Ubuntu 24.04.5 LTS (noble) | 8.5.0-2ubuntu10.9 | [libcurl4t64 8.5.0-2ubuntu10.9](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libcurl4t64-8.5.0-2ubuntu10.9.md) | May 15, 2026 |
| Linux | libcurl4t64 Ubuntu 25.10 (questing) | 8.14.1-2ubuntu1.3 | [libcurl4t64 8.14.1-2ubuntu1.3](https://patchblox.com/security/data/fix/linux/ubuntu-questing-libcurl4t64-8.14.1-2ubuntu1.3.md) | May 15, 2026 |
| Linux | libcurl4t64 Ubuntu 26.04.1 LTS (resolute) | 8.18.0-1ubuntu2.1 | [libcurl4t64 8.18.0-1ubuntu2.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libcurl4t64-8.18.0-1ubuntu2.1.md) | Apr 29, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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