Vulnerability · Published May 13, 2026 · Assigned by curl
CVE-2026-6253proxy credentials leak over redirect-to proxy
Medium 5.9
In plain English
A medium-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 0.7% (higher than 54% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | curl | 8.12.1-4.el10_2.7 | ALSA-2026:80512 |
| AlmaLinux:10 | libcurl | 8.12.1-4.el10_2.7 | ALSA-2026:80512 |
| AlmaLinux:10 | libcurl-devel | 8.12.1-4.el10_2.7 | ALSA-2026:80512 |
| AlmaLinux:10 | libcurl-minimal | 8.12.1-4.el10_2.7 | ALSA-2026:80512 |
| Alpine:v3.21 | curl | 8.14.1-r3 | ALPINE-CVE-2026-6253 |
| Alpine:v3.22 | curl | 8.14.1-r4 | ALPINE-CVE-2026-6253 |
| Alpine:v3.23 | curl | 8.20.0-r0 | ALPINE-CVE-2026-6253 |
| Alpine:v3.24 | curl | 8.20.0-r0 | ALPINE-CVE-2026-6253 |
| Debian:12 | curl | no fix listed | DEBIAN-CVE-2026-6253 |
| Debian:13 | curl | 8.14.1-2+deb13u4 | DEBIAN-CVE-2026-6253 |
| Debian:14 | curl | 8.20.0~rc3-1 | DEBIAN-CVE-2026-6253 |
| Rocky Linux:10 | curl | 0:8.12.1-4.el10_2.7 | RLSA-2026:80512 |
| Ubuntu:22.04:LTS | curl | 7.81.0-1ubuntu1.24 | UBUNTU-CVE-2026-6253 |
| Ubuntu:24.04:LTS | curl | 8.5.0-2ubuntu10.9 | UBUNTU-CVE-2026-6253 |
| Ubuntu:25.10 | curl | 8.14.1-2ubuntu1.3 | UBUNTU-CVE-2026-6253 |
| Ubuntu:26.04:LTS | curl | 8.18.0-1ubuntu2.1 | UBUNTU-CVE-2026-6253 |
Affected products (as reported)
Weakness: CWE-522 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H