Open Redirect via Origin Validation Bypass in better-auth

better-auth versions before 1.1.20 contain a bypass vulnerability in trustedOrigins validation logic affecting absolute URLs and wildcard domains. Attackers can construct malicious callbackURL parameters that pass origin checks and trigger open redirects to steal sensitive tokens for account takeover.

Casky was already ahead

This CVE exploits attack patterns that Casky's 322matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

CVE-2025-71403 exploits a flaw in better-auth's trustedOrigins validation logic where absolute URLs and wildcard domain patterns are incorrectly processed, allowing attackers to craft malicious callbackURL parameters that bypass security checks. This vulnerability enables open redirect attacks that can redirect users to attacker-controlled domains after authentication, enabling token theft and account takeover. Any application using better-auth versions before 1.1.20 for OAuth flows or callback handling is at risk, particularly those serving multiple domains or using wildcard origin configurations.

Casky's 322 matching skills leverage Claude's extended reasoning to correlate attack patterns across Initial Access (TA0001) and Credential Access (TA0043) techniques. Practitioners using the platform would see detections flagging suspicious callback parameter manipulation, origin validation bypass attempts, and redirect chain patterns that deviate from expected authentication flows. The skills map specific indicators—such as callbackURL parameters containing external domains, regex manipulation in origin checks, and token leakage POST-redirect sequences—to the underlying CWE-601 weakness, enabling teams to identify exploitation attempts in real time and trace them back to the vulnerable validation logic before tokens are compromised.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

322 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2025-71403.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2025-71403

Casky has 322 skills that investigate the attack patterns behind CVE-2025-71403. Run one and get CVSS-scored findings in 3 minutes.

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