CVE-2026-75899 fast-uri CVE debrief

Who should care

Developers and administrators using the fast-uri library in Node.js applications should be aware of this vulnerability and take immediate action to upgrade to a patched version. The vulnerability can have a significant impact on the security of applications that use the fast-uri library, particularly those that handle sensitive data or are exposed to the internet. Affected operator, platform, vulnerability-management, and security-team impact should be carefully assessed to ensure that all necessary precautions are taken. Compensating controls, such as monitoring and detection, should be implemented to mitigate the risk of exploitation. Additionally, asset inventory and rollback/change windows should be reviewed to ensure that all affected systems are properly managed and secured. Source tracking and exposure review are also essential to prevent potential security breaches. Security teams should review the vulnerability details and assess the potential impact on their organization's applications and infrastructure. They should also plan vendor-supported updates or mitigations through normal change control where exposure is confirmed. Furthermore, they should check relevant monitoring, detection, and logs for exposed assets that need extra review and track exceptions, retest remediated assets, and close the item only after evidence is documented. The goal is to minimize the risk of exploitation and ensure the security of applications and infrastructure. Therefore, it is crucial to take immediate action to address this vulnerability and prevent potential security breaches. The affected versions are 2.4.1 up to but not including 2.4.5, 3.1.2 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which normalize percent escapes once and preserve encoded percent signs. Users should upgrade to a patched version to prevent server-side request forgery and host-policy bypass vulnerabilities. Validate and normalize untrusted HTTP-family URIs before outbound routing, redirect validation, or host-policy checks. Implement compensating controls to monitor and track potential security breaches. Review compensating

Technical summary

The fast-uri library for Node.js has a vulnerability where it decodes percent escapes in a hostname during parsing and then decodes the parsed hostname a second time during authority recomposition. This can lead to a server-side request forgery and host-policy bypass primitive. The affected versions are 2.4.1 up to but not including 2.4.5, 3.1.2 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which normalize percent escapes once and preserve encoded percent signs.

Defensive priority

Server-side request forgery and host-policy bypass vulnerabilities in fast-uri library require immediate attention to prevent potential security breaches.

Recommended defensive actions

• Upgrade to a patched version of fast-uri (2.4.5, 3.1.6, or 4.1.3) to prevent server-side request forgery and host-policy bypass vulnerabilities.
• Validate and normalize untrusted HTTP-family URIs before outbound routing, redirect validation, or host-policy checks.
• Implement compensating controls to monitor and track potential security breaches.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.

Evidence notes

The fast-uri library for Node.js has a vulnerability where it decodes percent escapes in a hostname during parsing and then decodes the parsed hostname a second time during authority recomposition. This can lead to a server-side request forgery and host-policy bypass primitive. The affected versions are 2.4.1 up to but not including 2.4.5, 3.1.2 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3.

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.