better-auth before 1.6.11 Insecure Cryptographic Defaults via oidcProvider

published 2026-07-07 4 mo ago modified 2026-09-08 2 mo ago also GHSA-9h47-pqcx-hjr4 , EUVD-2026-51816

cvss: 8.7; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits: 0; none known

better-auth versions before 1.6.11 contain insecure cryptographic defaults in the oidcProvider and mcp plugins that advertise the none algorithm and accept plain PKCE by default. Attackers can exploit algorithm negotiation to accept unsigned tokens or intercept authorization codes when PKCE plain is used instead of the required S256 method.

Patch / fix

fixed in 2 links 1

npm better-auth 1.6.11
better-auth better-auth 1.6.11

github.com/better-auth/better-auth/releases/tag/v1.6.11 release

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 3 mo ago (2026-08-03)

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	9.4	CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N
CNA	3.1	8.7	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
CNA	4.0	9.4	CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/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
GitHub	3.1	8.7	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Affected packages

ecosystem	package	affected	fixed in
npm	better-auth	<1.6.11	1.6.11

Affected products

better-auth better-auth

Classification

Weakness

CWE-327 Use of a Broken or Risky Cryptographic Algorithm
CWE-1188 Initialization of a Resource with an Insecure Default
CWE-757 Selection of Less-Secure Algorithm During Negotiation

References

github.com /better-auth/better-auth/security/advisories/GHSA-9h47-pqcx-hjr4
vendor-advisory, web
vulncheck.com /advisories/better-auth-before-insecure-cryptographic-defaults-via-oidcprovider
third-party-advisory
github.com /better-auth/better-auth
package
github.com /better-auth/better-auth/releases/tag/v1.6.11
web

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary