CVE-2026-6253 - Vulnerability Analysis

Overview

curl contains an authentication credential leak caused by passing credentials from a first proxy to a second proxy during scheme redirects, letting attackers potentially access unauthorized proxy credentials, exploit requires use of multiple proxies with different schemes and credentials.

Severity & Score

Impact

Attackers can obtain proxy credentials unintentionally leaked to a second proxy, risking unauthorized access.

Mitigation

Update to the latest curl version that fixes proxy credential leakage.

References

• https://curl.se/docs/CVE-2026-6253.html
• https://curl.se/docs/CVE-2026-6253.json
• https://hackerone.com/reports/3669637
• http://www.openwall.com/lists/oss-security/2026/04/29/11

Social Media Activity(1 post)

daniel:// stenberg://

@bagder

Apr 29, 2026

Out of the eight new #curl CVEs, four of them had existed in code for over twenty years when we published. CVE-2026-5545 clocks in at 22.75 years old CVE-2026-7168 at 21.91 years CVE-2026-6429 at 20.95 years CVE-2026-6253 at 20.66 years And yet CVE-2026-5545 only becomes the 5th oldest vulnerability ever found in curl so far.

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Related Resources

• Vulnerability Intelligence Dashboard
• Credential Scanner