Vulnerability Database

357,869

Total vulnerabilities in the database

Better Auth URL parameter HTML Injection (Reflected Cross-Site scripting) — better-auth

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Summary

The better-auth /api/auth/error page was vulnerable to HTML injection, resulting in a reflected cross-site scripting (XSS) vulnerability.

Details

The value of error URL parameter was reflected as HTML on the error page: https://github.com/better-auth/better-auth/blob/05ada0b79dbcac93cc04ceb79b23ca598d07830c/packages/better-auth/src/api/routes/error.ts#L81

PoC

https://demo.better-auth.com/api/auth/error?error=%3Cscript%3Ealert(1)%3C/script%3E

image

Impact

An attacker who exploited this vulnerability by coercing a user to visit a specially-crafted URL could execute arbitrary JavaScript in the context of the user's browser.

Because better-auth is a dependency of web applications, the impact of such a vulnerability is unknowable; it depends on the functionality of the application/site using better-auth. I have calculated the CVSS score assuming the hypothetical victim is an administrator with elevated permissions and access.

  • Published: Feb 5, 2025
  • Updated: Dec 10, 2025
  • GHSA: GHSA-9x4v-xfq5-m8x5
  • Severity: Medium
  • Exploit:
  • CISA KEV:

CVSS v3:

  • Severity: Unknown
  • Score:
  • AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

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