Better Auth before 1.4.5 Path Normalization Bypass via rou3

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Better Auth relies on better-call, which uses the rou3 router library. In affected versions of rou3, paths are normalized by removing empty segments, so /path, //path, and ///path resolve to the same route. In Better Auth versions prior to 1.4.5 (which bundles the fixed rou3), this can allow attackers to bypass disabledPaths configuration and path-based rate limits by submitting requests with extra slashes in the URL path. The issue does not apply in deployments where the proxy or platform normalizes URLs by collapsing multiple slashes.

Source published

2 Aug 2026 12:15:22 UTC

Source modified

8 Oct 2026 15:21:31 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.8 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N

CVSS 3.1 · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Better Auth relies on better-call, which uses the rou3 router library. In affected versions of rou3, paths are normalized by removing empty segments, so /path, //path, and ///path resolve to the same route. In Better Auth versions prior to 1.4.5 (which bundles the fixed rou3), this can allow attackers to bypass disabledPaths configuration and path-based rate limits by submitting requests with extra slashes in the URL path. The issue does not apply in deployments where the proxy or platform normalizes URLs by collapsing multiple slashes.

Source published

Aug 2, 2026, 12:15:22 PM (timezone not stated)

Source modified

Oct 8, 2026, 3:21:31 PM (timezone not stated)

Observed here

9 Nov 2026 04:13:20 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.8 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N

Better Auth relies on better-call, which uses the rou3 router library. In affected versions of rou3, paths are normalized by removing empty segments, so /path, //path, and ///path resolve to the same route. In Better Auth versions prior to 1.4.5 (which bundles the fixed rou3), this can allow attackers to bypass disabledPaths configuration and path-based rate limits by submitting requests with extra slashes in the URL path. The issue does not apply in deployments where the proxy or platform normalizes URLs by collapsing multiple slashes.

Source published

2 Aug 2026 13:16:52 UTC

Source modified

8 Oct 2026 16:16:53 UTC

Observed here

25 Oct 2026 04:17:18 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.8 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

## Summary An issue in the underlying router library **rou3** can cause `/path` and `//path` to be treated as identical routes. If your environment does **not** normalize incoming URLs (e.g., by collapsing multiple slashes), this can allow bypasses of `disabledPaths` and path-based rate limits. ## Details Better Auth uses **better-call**, which internally relies on **rou3** for routing. Affected versions of rou3 normalize paths by removing empty segments. As a result: * `/sign-in/email` * `//sign-in/email` * `///sign-in/email` …all resolve to the same route. Some production setups *automatically* collapse multiple slashes. This includes: * Vercel with Nextjs (default) * Cloudflare - when normalize to urls origin is enabled (https://developers.cloudflare.com/rules/normalization/settings/#normalize-urls-to-origin) In these environments and other configurations where `//path` reach Better Auth as `/path`, the issue does not apply. ## Fix Updating rou3 to the latest version resolves the issue: * better-call previously depended on `"rou3": "^0.5.1"` * The fix was introduced after that version (commit: [https://github.com/h3js/rou3/commit/f60b43fa648399534507c9ac7db36d705b8874c3](https://github.com/h3js/rou3/commit/f60b43fa648399534507c9ac7db36d705b8874c3)) Better Auth recommends: 1. **Upgrading to Better Auth v1.4.5 or later**, which includes the updated rou3. 2. Ensuring the proxy normalizes URLs. 3. If project maintainers cannot upgrade yet, they can protect their app by normalizing url before it reaches better-auth handler. See example below: ```ts const req = new Request(...) // this would be the actual request object const url = new URL(req.url); const normalizedPath = url.pathname.replace(/\/+/g, "/"); if (url.pathname !== normalizedPath) { url.pathname = normalizedPath; // Update the raw request pathname Object.defineProperty(req, "url", { value: url.toString(), writable: true, configurable: true, }); } ``` ## Impact * Bypass `disabledPaths` * Bypass path-based rate limits The impact of bypassing disabled paths could vary based on a project's configuration.

Source published

16 Dec 2025 21:22:45 UTC

Source modified

3 Aug 2026 03:41:44 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Publisher rating · HIGH