VulnerabilityPublished 4 Nov 2026

CVE-2026-121802: Better Auth · Origin Validation Error

Affects Better AuthSource CVE Database V5

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Not known to be exploited · CVSS 9.1 Critical : upgrade to 1.7.16 as a priority.

Data as of 4 Nov 2026, 03:13 UTC

CVSS 3.1 base score

9.1Critical

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (mitre)	CVSS 3.1	9.1

Patch: Available – fixed in 1.7.16

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 3 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Better Auth to 1.7.16.

Affected software

Product	Affected	Fixed in
better-authBetter Auth	Affected <1.7.16	Fixed in 1.7.16
npmBetter Auth`pkg:npm/Better Auth`Other threats	Affected <1.7.16	Fixed in 1.7.16

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade to better-auth Better Auth version 1.7.16 or later to apply the official fix. After updating, rotate the application secret as recommended by the vendor to prevent misuse of previously issued tokens or state values.

Description

CVE-2026-121802 is a critical vulnerability in better-auth's Better Auth package versions before 1.7.16. It involves an origin validation error (CWE-346) where the software signs a caller-supplied state value without verifying if it was issued by the server. This flaw allows unauthenticated attackers to perform account takeover actions, such as changing any account's email address. The issue is fixed in version 1.7.16. After updating, the application secret must be rotated to ensure security.

Impact

Exploitation of this vulnerability can lead to account takeover scenarios, allowing unauthenticated attackers to change any user's email address. This compromises account integrity and user security. The CVSS score of 9.1 reflects high confidentiality and integrity impact with no required privileges or user interaction.

Summary

The vulnerability in better-auth's Better Auth package (versions >=0 and <1.7.16) stems from improper origin validation (CWE-346). Specifically, the software signs a state parameter supplied by the caller without confirming that the state was originally issued by the server. This flaw enables attackers to bypass authentication controls and perform unauthorized changes to user accounts, including changing email addresses without authentication. The vulnerability has a CVSS v3.1 score of 9.1, indicating critical severity. The issue is resolved in version 1.7.16, and rotating the application secret after patching is required to fully mitigate the risk.

CWE-346Origin Validation Error (opens in a new tab)
Class weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
The product does not properly verify that the source of data or communication is valid.
OWASP Cheat Sheets
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V14.5.2 (opens in a new tab)
V14.5.3 (opens in a new tab)
V1.4.4 (opens in a new tab)
Attack patterns
JSON Hijacking (aka JavaScript Hijacking) (opens in a new tab)
Cache Poisoning (opens in a new tab)
DNS Cache Poisoning (opens in a new tab)
Exploit Script-Based APIs (opens in a new tab)
Application API Message Manipulation via Man-in-the-Middle (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2026, 02:59 UTC

WeaknessesCWE-346

Technical details

References

Community reviews

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