What’s Vulnerable › Vulnerabilities

CVE-2026-8286: wrong STARTTLS connection reuse

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-03 · updated 2026-09-15
• Weakness: CWE-295

Description

A vulnerability exists where a new transfer that uses STARTTLS to upgrade the connection might reuse an existing live connection even though the TLS configuration mismatches so it should not.

Affected products

• curl: from 7.30.0 before 8.21.0 — fixed in 8.21.0

How to fix

Upgrade to a fixed version: curl 8.21.0. Check the vendor advisory for mitigations.

References

• https://curl.se/docs/CVE-2026-8286.html
• https://curl.se/docs/CVE-2026-8286.json
• https://hackerone.com/reports/3718195
• https://hackerone.com/reports/3718195

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