CVE-2025-27143 — better-auth
Fix: better-auth/better-auth@24659aeCVE-2025-27143 is a Open Redirect vulnerability in better-auth. A fix is available for better-auth — see the affected versions and patch details below.
Beter Auth has an Open Redirect via Scheme-Less Callback Parameter
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-27143.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
better-authnpmDescription
Summary
The application is vulnerable to an open redirect due to improper validation of the callbackURL parameter in the email verification endpoint and any other endpoint that accepts callback url. While the server blocks fully qualified URLs (e.g., https://evil.com), it incorrectly allows scheme-less URLs (e.g., //malicious-site.com). This results in the browser interpreting the URL as https://malicious-site.com, leading to unintended redirection.
bypass for : https://github.com/better-auth/better-auth/security/advisories/GHSA-8jhw-6pjj-8723
Affected Versions
All versions prior to 1.1.19
Details
The application’s email verification endpoint (/auth/verify-email) accepts a callbackURL parameter intended to redirect users after successful email verification. While the server correctly blocks fully qualified external URLs (e.g., https://evil.com), it improperly allows scheme-less URLs (e.g., //malicious-site.com). This issue occurs because browsers interpret //malicious-site.com as https://malicious-site.com, leading to an open redirect vulnerability.
An attacker can exploit this flaw by crafting a malicious verification link and tricking users into clicking it. Upon successful email verification, the user will be automatically redirected to the attacker's website, which can be used for phishing, malware distribution, or stealing sensitive authentication tokens.
Impact
Phishing & Credential Theft – Attackers can redirect users to a fake login page, tricking them into entering sensitive credentials, which can then be stolen.
Session Hijacking & Token Theft – If used in OAuth flows, an attacker could redirect authentication tokens to their own domain, leading to account takeover.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | better-auth | all versions | 1.1.20npm install better-auth@1.1.20 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for better-auth, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update better-auth to 1.1.20 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-27143 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-27143 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-27143. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-27143 in your dependencies?
O3 Security finds CVE-2025-27143 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.