What’s Vulnerable › Vulnerabilities

CVE-2026-19931: Negotiate ambient user conn reuse

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.1% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-09-06 · updated 2026-09-15
• Weakness: CWE-488

Description

A flaw in libcurl makes it wrongly reuse an HTTP connection setup for a given hostname using Negotiate authentication, when the initial request is done using empty credentials. This can make user B's request get sent over user A's previously authenticated connection.

Affected products

• curl: from 7.64.1 before 8.22.0 — fixed in 8.22.0

How to fix

Upgrade to a fixed version: curl 8.22.0. Check the vendor advisory for mitigations.

References

• https://curl.se/docs/CVE-2026-19931.html
• https://curl.se/docs/CVE-2026-19931.json
• https://hackerone.com/reports/3923520
• https://hackerone.com/reports/3923520

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