{"id":"CVE-2026-54238","kind":"vulnerability","aliases":["CVE-2026-54238"],"related":[],"title":"Supabase Realtime: expired JWT accepted when exp is a string","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.","summary":"Supabase Realtime's REST broadcast endpoints accept an expired JWT when its exp claim is encoded as a JSON string rather than a number. An attacker holding such a token can push broadcast messages to subscribers of a project.","severity":"low","cvss":3.1,"epss":0.00206,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["realtime","runtime","self-hosted","supabase","websockets"],"not_affected_if":["patched-version"],"how_to_check":"- Check the Supabase Realtime server version and compare it with `2.103.1`\n- Review whether the project uses the REST broadcast endpoints (unknown if the sources say more)","fix":"- Upgrade Supabase Realtime to `2.103.1` or later","status":"open","published_at":"2026-10-22T18:17:28+00:00","first_seen_at":"2026-10-23T21:57:31+00:00","triaged_at":"2026-10-25T04:47:20+00:00","updated_at":"2026-10-25T04:47:20+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-10-25T04:47:20Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade Supabase Realtime to `2.103.1` or later","reach":"internet","title":"Supabase Realtime: expired JWT accepted when exp is a string","impact":"low","summary":"Supabase Realtime's REST broadcast endpoints accept an expired JWT when its exp claim is encoded as a JSON string rather than a number. An attacker holding such a token can push broadcast messages to subscribers of a project.","category":"runtime","nicknames":[],"who_cares":["supabase","realtime","websockets","self-hosted"],"confidence":0.6,"needs_auth":"yes","worst_case":"Attacker sends fake broadcast messages to realtime subscribers","analyst_note":"Confirm whether managed Supabase instances were patched and whether the broadcast endpoints are on by default; check the NVD entry for affected version range.","how_to_check":"- Check the Supabase Realtime server version and compare it with `2.103.1`\n- Review whether the project uses the REST broadcast endpoints (unknown if the sources say more)","needs_analyst":true,"not_affected_if":["patched-version"],"who_is_affected":"Projects running Supabase Realtime before version `2.103.1` that use the REST broadcast endpoints. The sources do not say whether managed Supabase hosting has already applied the patch, so self-hosted deployments are the clearest case. Applications that do not use broadcast messages are less exposed.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"low"},"cost_usd":0.000612,"input_tokens":3482,"output_tokens":527,"severity_before":"low"},"analyst_status":null,"analyst_note":null,"search":"'-2026':12A,15A '-54238':13A,16A '2.103.1':76C,168C '202':119C 'accept':5A,30B,81C,116C 'allow':128C 'applic':159C 'attack':49B,131C,139C 'broadcast':28B,56B,66C,79C,123C,133C,154C 'chang':70C 'claim':37B,88C 'could':127C 'cve':11A,14A 'emit':121C 'encod':39B,90C 'endpoint':29B,80C 'exp':7A,36B,87C,107C 'expir':3A,32B,83C,105C 'hold':50B 'host':21B 'impact':152C 'instead':95C 'integ':106C 'internet/only':145C 'issu':162C 'json':42B,93C,98C 'jwt':4A,33B,84C 'messag':57B,135C,155C 'number':47B,99C 'patch':165C 'perform':142C 'postgr':69C 'presenc':67C 'prior':73C 'project':62B,150C 'provid':65C 'push':55B 'rather':44B 'realtim':2A,17B,25B,64C,134C 'reject':103C 'request':117C 'rest':27B,78C 'return':118C 'rout':102C 'runtim':18B 'secret':114C 'self':20B 'self-host':19B 'sign':109C 'specif':160C 'string':10A,43B,94C 'subscrib':59B,125C,137C,157C 'supabas':1A,22B,24B,63C,149C 'tenant':113C 'token':53B,108C 'unauthent':130C 'version':75C,167C 'via':71C,143C 'websocket':23B,72C 'within':147C","nicknames":[],"mitigations":[],"who_affected":"Projects running Supabase Realtime before version `2.103.1` that use the REST broadcast endpoints. The sources do not say whether managed Supabase hosting has already applied the patch, so self-hosted deployments are the clearest case. Applications that do not use broadcast messages are less exposed.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-22T18:17:28+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N","cvss_by":"security-advisories@github.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-54238","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54238","severity":null,"published_at":"2026-10-22T18:17:28+00:00","modified_at":"2026-10-23T19:42:24+00:00","first_seen_at":"2026-10-23T21:57:31+00:00","fetched_at":"2026-10-23T22:29:02+00:00","note":null},{"source":"epss","external_id":"CVE-2026-54238","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-54238","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-24T07:15:51+00:00","fetched_at":"2026-10-24T07:15:51+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}