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TI-2026-33155 Aliases CVE-2026-45364GHSA-p6v2-xcpg-h6xw

Better Auth: Rate limiter keys IPv6 addresses individually and is bypassable via prefix rotation

Priority LOW 38CWE-307Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
Low · Low · Low
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-307.

Summary

Better Auth is an authentication and authorization library for TypeScript. Prior to 1.4.17 and 1.5.0-beta.9, Better Auth's HTTP rate limiter keyed each request by the exact textual IP address it received in x-forwarded-for (or the configured IP-bearing header). IPv6 clients controlling a typical /64 allocation could rotate through 2^64 distinct source addresses without exhausting the per-address counter, defeating rate limiting on /sign-in/email, /sign-up/email, /forget-password, and every other path the limiter protects. The same bug allowed a single client to vary the textual encoding of one IPv6 address (uppercase, compression, IPv4-mapped, hex-encoded IPv4-in-IPv6) and produce multiple distinct keys. This vulnerability is fixed in 1.4.17 and 1.5.0-beta.9.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00295 22nd percentileScored 2026-11-07
Fix Fixed better-auth (better-auth): 1.4.17, 1.5.0-beta.9better-auth (npm): 1.4.17, 1.5.0-beta.9

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
better-authbetter-authbefore 1.4.17; 1.5.0-beta.1 to before 1.5.0-beta.91.4.17, 1.5.0-beta.9Patch availableCNA
—better-auth (npm)before 1.4.171.4.17Patch availableGHSA-p6v2-xcpg-h6xw
—better-auth (npm)1.5.0-beta.1 to before 1.5.0-beta.91.5.0-beta.9Patch availableGHSA-p6v2-xcpg-h6xw
  • better-auth Vendorbetter-auth Affected before 1.4.17; 1.5.0-beta.1 to before 1.5.0-beta.9 Fixed in 1.4.17, 1.5.0-beta.9 Patch available CNA
  • better-auth (npm) Vendor— Affected before 1.4.17 Fixed in 1.4.17 Patch available GHSA-p6v2-xcpg-h6xw
  • better-auth (npm) Vendor— Affected 1.5.0-beta.1 to before 1.5.0-beta.9 Fixed in 1.5.0-beta.9 Patch available GHSA-p6v2-xcpg-h6xw

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:better-auth:better_auth:*:*:*:*:*:*:*:*——better-auth
  • cpe:2.3:a:better-auth:better_auth:*:*:*:*:*:*:*:* Versions — — ·better-auth

Remediation

  • Fix · CNA better-auth (better-auth) Fixed in 1.4.17, 1.5.0-beta.9
  • Fix · GHSA-p6v2-xcpg-h6xw better-auth (npm) Fixed in 1.4.17 Advisory →
  • Fix · GHSA-p6v2-xcpg-h6xw better-auth (npm) Fixed in 1.5.0-beta.9 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-45364
  2. 2026-10-03 Alias added: GHSA-p6v2-xcpg-h6xw

References

Advisory 1

Other 6

  • TI-2025-38277 Better Auth: Unauthenticated API key creation through api-key plugin CVSS 4.0CRITICAL 9.3
  • TI-2026-47627 better-auth SCIM 1.5.0 before 1.7.0-beta.4 Authorization Bypass CVSS 4.0HIGH 8.7
  • TI-2025-20000 Beter Auth has an Open Redirect via Scheme-Less Callback Parameter CVSS 4.0MEDIUM 6.9
  • TI-2026-13066 better-auth better-icons scan_project_icons/sync_icon path traversal CVSS 4.0MEDIUM 4.8
  • TI-2026-79320 OAuth state accepted as Magic Link token in Better Auth CVSS 3.1CRITICAL 9.1
  • TI-2026-74552 Authentication bypass in Better Auth Magic Link verification CVSS 4.0CRITICAL 9.3
See all 39 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences