CVE-2026-1965 curl CVE debrief

Who should care

Defenders responsible for applications using libcurl with Negotiate authentication should assess exposure and prioritize remediation. This includes reviewing inventory, updating vulnerable systems, and applying mitigations.

Why it matters

CVE-2026-1965 is a medium-severity vulnerability in libcurl that can lead to authentication bypass when using Negotiate authentication. Defenders should assess exposure, prioritize remediation, and update or patch vulnerable systems to prevent potential unauthorized access.

• Potential authentication bypass in applications using libcurl with Negotiate authentication
• Possible unauthorized access to sensitive data or systems
• Need for verification of inventory and remediation of vulnerable systems
• Importance of updating or patching libcurl to prevent exploitation

Technical summary

libcurl's connection reuse feature can lead to authentication bypass when using Negotiate authentication. An application may reuse a connection authenticated with different credentials, potentially allowing unauthorized access. This issue arises from a logical error in the code that manages connection reuse. Affected products and deployments should be verified for exposure. Defenders should review inventory and update vulnerable systems to prevent potential unauthorized access. The vulnerability has a medium severity and a CVSS score of 6.5.

Defensive priority

Defenders should assess exposure and prioritize verification of inventory, especially for applications using libcurl with Negotiate authentication. Remediation involves updating to a fixed version or applying mitigations.

Recommended defensive actions

• Assess exposure by verifying if applications using libcurl are configured for Negotiate authentication
• Update libcurl to a version that fixes the issue
• Apply mitigations by setting CURLOPT_FRESH_CONNECT, CURLOPT_MAXCONNECTS, or CURLMOPT_MAX_HOST_CONNECTIONS
• Review and update inventory of affected systems
• Perform vulnerability scanning to identify potentially exposed assets
• Implement compensating controls for exposed systems while remediation is scheduled
• Monitor relevant systems for suspicious activity

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and affected versions. Vendor advisories offer patches and mitigations. Affected products and deployments using libcurl with Negotiate authentication should be verified for exposure. Defenders should review inventory, update vulnerable systems, and apply mitigations. Evidence limits suggest verifying specific versions and configurations.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.