What’s Vulnerable › Vulnerabilities

CVE-2026-86411: FTP connection reuse inherits client-certificate

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-20 · updated 2026-10-29
• Weakness: CWE-488

Description

An `ftp://` transfer configured with `CURLUSESSL_NONE` can reuse a pooled FTP control connection that a previous easy handle upgraded with `STARTTLS` and authenticated using a client certificate. The second handle performs neither a new TLS handshake nor a new FTP login, so the server continues to authorize it under the first handle's certificate identity.

Affected products

• curl: from 8.21.0 through 8.21.0

References

• https://curl.se/docs/CVE-2026-86411.html
• https://curl.se/docs/CVE-2026-86411.json
• https://hackerone.com/reports/3973190
• https://hackerone.com/reports/3973190

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