{"id":"CVE-2026-109924","kind":"vulnerability","aliases":["CVE-2026-109924","GHSA-4qv8-2p9j-2685"],"related":[],"title":"undici vulnerable to Denial of Service via unbounded memory in the EventSource parser","description":"undici is an HTTP client library for Node.js. In versions 6.5.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its EventSource client can be driven to exhaust process memory by a malicious or compromised Server-Sent Events peer. By sending millions of tiny completed data fields with no blank event separator, or a single unfinished line split across many chunks, the parser retains a growing amount of per-field and per-chunk state that the byte-based maxEventSize and maxResponseSize limits do not bound, and because maxResponseSize is enforced on the compressed body before decompression, a small compressed response can expand into enough retained memory to terminate the process. An application only needs to maintain an EventSource connection to an untrusted peer, which controls only the response, and availability is the only impact. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which bound the retained parser state independently of the byte limits, and users should upgrade to one of those versions or later. There is no workaround.","summary":"The undici HTTP client for Node.js keeps growing parser state while reading Server-Sent Events, so a malicious or compromised SSE server can drive memory use up. A small compressed response can expand into enough retained memory to crash the process, which is a denial of service with no code execution.","severity":"high","cvss":7.5,"epss":0.00321,"exploited":false,"exploited_at":null,"products":[{"name":"undici","fixed":["6.29.1"],"affected":">= 6.5.0, < 6.29.1","ecosystem":"npm"},{"name":"undici","fixed":["7.30.1"],"affected":">= 7.0.0, < 7.30.1","ecosystem":"npm"},{"name":"undici","fixed":["8.12.2"],"affected":">= 8.0.0, < 8.12.2","ecosystem":"npm"},{"name":"nodejs undici","fixed":["6.29.1"],"affected":">= 6.5.0, < 6.29.1","ecosystem":"vendor"},{"name":"nodejs undici","fixed":["7.30.1"],"affected":">= 7.0.0, < 7.30.1","ecosystem":"vendor"},{"name":"nodejs undici","fixed":["8.12.2"],"affected":">= 8.0.0, < 8.12.2","ecosystem":"vendor"}],"ecosystems":["npm","vendor"],"tags":["backend","cwe-770","node.js","npm","package","undici"],"not_affected_if":["no-eventsource-usage","trusted-peers-only"],"how_to_check":"- Run `node -p \"require('undici/package.json').version\"` in each project that depends on undici, and check whether the output falls in an affected range (6.5.0 to 6.29.0, 7.0.0 to 7.30.0, or 8.0.0 to 8.12.1).\n- Search code for `EventSource` from undici to see whether the application keeps SSE connections open to peers it does not control.","fix":"- Upgrade undici to `6.29.1`, `7.30.1`, or `8.12.2` (or later in the same major line).\n- No workaround is documented by the sources; upgrading is the fix.","status":"open","published_at":"2026-10-15T19:17:22+00:00","first_seen_at":"2026-10-23T22:15:56+00:00","triaged_at":"2026-10-25T03:25:23+00:00","updated_at":"2026-10-25T03:25:23+00:00","category":"package","confidence":0.85,"triage":{"at":"2026-10-25T03:25:23Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade undici to `6.29.1`, `7.30.1`, or `8.12.2` (or later in the same major line).\n- No workaround is documented by the sources; upgrading is the fix.","reach":"internet","title":"undici: EventSource parser lets a malicious server exhaust process memory","impact":"low","summary":"The undici HTTP client for Node.js keeps growing parser state while reading Server-Sent Events, so a malicious or compromised SSE server can drive memory use up. A small compressed response can expand into enough retained memory to crash the process, which is a denial of service with no code execution.","category":"package","nicknames":[],"who_cares":["node.js","undici","npm","backend"],"confidence":0.85,"needs_auth":"no","worst_case":"Malicious SSE server crashes the Node.js process via memory exhaustion","analyst_note":"","how_to_check":"- Run `node -p \"require('undici/package.json').version\"` in each project that depends on undici, and check whether the output falls in an affected range (6.5.0 to 6.29.0, 7.0.0 to 7.30.0, or 8.0.0 to 8.12.1).\n- Search code for `EventSource` from undici to see whether the application keeps SSE connections open to peers it does not control.","needs_analyst":false,"not_affected_if":["no-eventsource-usage","trusted-peers-only"],"who_is_affected":"Applications that open an EventSource connection with undici to a server they do not fully trust, such as third-party streams, webhooks or remote APIs, are exposed, because the peer controls the response. Projects that use undici only for ordinary requests to their own services, or that never open EventSource connections, are less exposed, though upgrading still closes the gap.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"high"},"cost_usd":0.000698,"input_tokens":3837,"output_tokens":628,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-109924':16A,24A '-2026':15A,23A '-770':36B '2685':21A '2p9j':20A '4qv8':19A '6.29.0':105C '6.29.1':237C '6.5.0':103C '7.0.0':106C '7.30.0':108C '7.30.1':238C '8.0.0':110C '8.12.1':112C '8.12.2':240C 'across':152C 'amount':160C 'applic':208C 'avail':226C 'backend':34B 'base':174C 'blank':143C 'bodi':190C 'bound':181C,242C 'byte':173C,250C 'byte-bas':172C 'chunk':154C,168C 'client':44B,97C,115C 'code':91B 'complet':138C 'compress':71B,189C,195C 'compromis':61B,127C 'connect':215C 'control':221C 'crash':80B 'cve':14A,22A 'cwe':35B 'data':139C 'decompress':192C 'denial':4A,86B 'drive':65B 'driven':118C 'enforc':186C 'enough':76B,200C 'event':56B,131C,144C 'eventsourc':12A,114C,214C 'execut':92B 'exhaust':120C 'expand':74B,198C 'field':140C,164C 'fix':234C 'ghsa':18A 'ghsa-4qv8-2p9j':17A 'grow':48B,159C 'http':43B,96C 'impact':230C 'independ':247C 'issu':232C 'keep':47B 'later':262C 'librari':98C 'limit':178C,251C 'line':150C 'maintain':212C 'malici':59B,125C 'mani':153C 'maxevents':175C 'maxresponses':177C,184C 'memori':9A,66B,78B,122C,202C 'million':135C 'need':210C 'node.js':37B,46B,100C 'nodejs':28A,30A,32A 'npm':38B 'one':257C 'packag':39B 'parser':13A,49B,156C,245C 'peer':132C,219C 'per':163C,167C 'per-chunk':166C 'per-field':162C 'process':82B,121C,206C 'read':52B 'respons':72B,196C,224C 'retain':77B,157C,201C,244C 'send':134C 'sent':55B,130C 'separ':145C 'server':54B,63B,129C 'server-s':53B,128C 'servic':6A,88B 'singl':148C 'small':70B,194C 'split':151C 'sse':62B 'state':50B,169C,246C 'termin':204C 'tini':137C 'unbound':8A 'undici':1A,25A,26A,27A,29A,31A,33A,40B,42B,93C,236C 'unfinish':149C 'untrust':218C 'upgrad':255C 'use':67B 'user':253C 'version':102C,260C 'via':7A 'vulner':2A 'workaround':266C","nicknames":[],"mitigations":[],"who_affected":"Applications that open an EventSource connection with undici to a server they do not fully trust, such as third-party streams, webhooks or remote APIs, are exposed, because the peer controls the response. Projects that use undici only for ordinary requests to their own services, or that never open EventSource connections, are less exposed, though upgrading still closes the gap.","tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-15T19:17:22+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","cvss_by":"GitHub","poc_count":0,"sources":[{"source":"ghsa","external_id":"GHSA-4qv8-2p9j-2685","url":"https://github.com/advisories/GHSA-4qv8-2p9j-2685","severity":"medium","published_at":"2026-10-23T22:13:29+00:00","modified_at":"2026-10-23T22:13:31+00:00","first_seen_at":"2026-10-23T22:15:56+00:00","fetched_at":"2026-10-23T22:15:56+00:00","note":null},{"source":"nvd","external_id":"CVE-2026-109924","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-109924","severity":null,"published_at":"2026-10-15T19:17:22+00:00","modified_at":"2026-10-19T20:45:00+00:00","first_seen_at":"2026-10-23T23:44:52+00:00","fetched_at":"2026-10-23T23:44:52+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"}