What’s Vulnerable › Vulnerabilities

CVE-2026-87861: cross-origin reuse of a Negotiate connection

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-20 · updated 2026-10-30
• Weakness: CWE-201

Description

When using ambient user credentials, an HTTP request directed to one origin may be dispatched over a connection previously authenticated via Negotiate for a different origin, leaving the request's intended credentials unused.

Affected products

• curl: from 8.22.0 through 8.22.0; from 8.21.0 through 8.21.0

References

• https://curl.se/docs/CVE-2026-87861.html
• https://curl.se/docs/CVE-2026-87861.json
• https://hackerone.com/reports/3972094
• https://hackerone.com/reports/3972094

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