CVE-2026-6253 Details
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
A vulnerability exists in curl and libcurl versions 7.14.1 through 8.19.0, where credentials for one proxy can be incorrectly forwarded to another proxy during a redirect. This issue arises when different proxies are used for different URL schemes, and the first proxy requires authentication while the second does not. When a redirect occurs from a URL using the first proxy to one using the second, the credentials for the first proxy can be sent to the second without any indication of their origin or validity.
Users are advised to upgrade to curl and libcurl version 8.20.0, or to apply the patch available in the curl GitHub repository.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed May 13, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
| URL | Source(s) | Tag(s) |
|---|---|---|
| https://hackerone.com/reports/3669637 | CISA-ADP | ExploitIssue TrackingThird Party Advisory |
| https://curl.se/docs/CVE-2026-6253.html | curl | PatchVendor Advisory |
| https://curl.se/docs/CVE-2026-6253.json | curl | Vendor Advisory |
| https://hackerone.com/reports/3669637 | curl | ExploitIssue TrackingThird Party Advisory |
| http://www.openwall.com/lists/oss-security/2026/04/29/11 | CVE | Mailing ListPatchThird Party Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-522 | Insufficiently Protected Credentials | [email protected] |
| CWE-522 | Insufficiently Protected Credentials | curl |
Affected Products
| Product | Versions |
|---|---|
| haxx curl | >= 7.14.1, < 8.20.0 |
CPE
Remediation
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Change History
9 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Sep 15, 2026 | CVE Modified | CISA-ADP |
| Sep 15, 2026 | CVE Modified | CVE |
| Sep 15, 2026 | CVE Modified | curl |
| Jun 17, 2026 | CVE Modified | curl |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 14, 2026 | Initial Analysis | [email protected] |
| May 13, 2026 | CVE Modified | CISA-ADP |
| May 13, 2026 | New CVE Received | curl |
| May 13, 2026 | CVE Modified | CVE |