CVE-2026-6253

proxy credentials leak over redirect-to proxy

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Published May 13, 2026 CVSS 3.1 · 5.9 Medium EPSS < 1% KEV · Not listed
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

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8227-1 curl vulnerabilities
History
Type Values Removed Values Added
First Time appeared Haxx
Haxx curl
Weaknesses CWE-522
CPEs cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:*
Vendors & Products Haxx
Haxx curl
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N'}

 ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}
Type Values Removed Values Added
References
Type Values Removed Values Added
Description A flaw was found in curl. When curl is configured to use distinct proxies for different URL schemes, a redirect from a URL using an authenticated proxy to one using an unauthenticated proxy can inadvertently expose the initial proxy's credentials. This improper credential management (CWE-522) may allow an attacker to gain unauthorized access or information by intercepting these disclosed credentials. 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
Title curl: curl: Proxy credential disclosure via redirects to unauthenticated proxies proxy credentials leak over redirect-to proxy
References
Type Values Removed Values Added
First Time appeared Curl
Curl curl
Vendors & Products Curl
Curl curl
Type Values Removed Values Added
Description A flaw was found in curl. When curl is configured to use distinct proxies for different URL schemes, a redirect from a URL using an authenticated proxy to one using an unauthenticated proxy can inadvertently expose the initial proxy's credentials. This improper credential management (CWE-522) may allow an attacker to gain unauthorized access or information by intercepting these disclosed credentials.
Title curl: curl: Proxy credential disclosure via redirects to unauthenticated proxies
Weaknesses CWE-201
References
Metrics threat_severity

None

 cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N'}

threat_severity

Moderate
Earlier changes (1)
Weaknesses

Sources

Status
PUBLISHED
Assigner
curl
Published
Updated
Sep 15, 2026, 6:03 AM
Reserved
Apr 13, 2026, 8:11 PM

View source JSON

Updated
May 13, 2026, 9:05 AM

JSON

Status
Modified
Published
May 13, 2026, 1:01 PM
Modified
Nov 11, 2026, 8:10 PM

View source JSON

Severity
Moderate
Public date
Apr 29, 2026, 12:00 AM

View source Bugzilla JSON

Updated
May 14, 2026, 3:15 PM

JSON