# CVE-2026-6253: proxy credentials leak over redirect-to proxy CVE-2026-6253 is fixed in 10 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: Routine. - Web page: https://patchblox.com/security/cve/CVE-2026-6253 - Priority: Routine - CVSS: 6.5 (Moderate) - EPSS: 0.0072 - 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-2026-6253 ## Description curl might erroneously pass on credentials for a first proxy to a second proxy. This can happen when the following conditions are true: 1. curl is setup to use specific different proxies for different URL schemes 2. the first proxy needs credentials 3. the second proxy uses no credentials 4. while using the first proxy (using say `http://`), curl is asked to follow a redirect to a URL using another scheme (say `https://`), accessed using a second, different, proxy ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | curl Debian 13.5 (trixie) | 8.14.1-2+deb13u4 | [DEBIAN-CVE-2026-6253](https://patchblox.com/security/data/fix/linux/debian-cve-2026-6253.md) | May 15, 2026 | | Linux | curl Debian 14 | 8.20.0~rc3-1 | [DEBIAN-CVE-2026-6253](https://patchblox.com/security/data/fix/linux/debian-cve-2026-6253.md) | May 15, 2026 | | Linux | curl RHEL 10 | 8.12.1-4.el10_2.7 | [RHSA-2026:80512](https://patchblox.com/security/data/fix/linux/rhsa-2026-80512.md) | Jul 3, 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 almalinux 10 | 8.12.1-4.el10_2.7 | [ALSA-2026:80512](https://patchblox.com/security/data/fix/linux/alsa-2026-80512.md) | Nov 7, 2026 | | Linux | curl ol 10 | 0:8.12.1-4.el10_2.7 | [ELSA-2026-80512](https://patchblox.com/security/data/fix/linux/elsa-2026-80512.md) | Nov 7, 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 rocky 10 | 0:8.12.1-4.el10_2.7 | [RLSA-2026:80512](https://patchblox.com/security/data/fix/linux/rlsa-2026-80512.md) | Nov 7, 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 | libcurl almalinux 10 | 8.12.1-4.el10_2.7 | [ALSA-2026:80512](https://patchblox.com/security/data/fix/linux/alsa-2026-80512.md) | Nov 7, 2026 | | Linux | libcurl ol 10 | 0:8.12.1-4.el10_2.7 | [ELSA-2026-80512](https://patchblox.com/security/data/fix/linux/elsa-2026-80512.md) | Nov 7, 2026 | | Linux | libcurl-devel almalinux 10 | 8.12.1-4.el10_2.7 | [ALSA-2026:80512](https://patchblox.com/security/data/fix/linux/alsa-2026-80512.md) | Nov 7, 2026 | | Linux | libcurl-devel ol 10 | 0:8.12.1-4.el10_2.7 | [ELSA-2026-80512](https://patchblox.com/security/data/fix/linux/elsa-2026-80512.md) | Nov 7, 2026 | | Linux | libcurl-minimal almalinux 10 | 8.12.1-4.el10_2.7 | [ALSA-2026:80512](https://patchblox.com/security/data/fix/linux/alsa-2026-80512.md) | Nov 7, 2026 | | Linux | libcurl-minimal ol 10 | 0:8.12.1-4.el10_2.7 | [ELSA-2026-80512](https://patchblox.com/security/data/fix/linux/elsa-2026-80512.md) | Nov 7, 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 | --- Data as of 2026-11-08T13:06:02Z UTC. 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