{"id":"CVE-2026-87029","kind":"vulnerability","aliases":["CVE-2026-87029","GHSA-55wc-3pg8-jfw6"],"related":[],"title":"undici vulnerable to Denial of Service via unhandled exception in the decompress interceptor","description":"## Impact\n\nundici's `decompress` interceptor forwards decompressed response data to the downstream handler from zlib stream event callbacks without catching exceptions those callbacks may throw. undici's engine converts a synchronous throw from a downstream handler into a per-request failure, but that protection is not in place when the throw happens asynchronously from a zlib callback. As a result, a downstream handler that throws by design, for example the built-in `dump` interceptor which throws when a response exceeds its `maxSize`, escapes as an uncaught exception and terminates the Node.js process.\n\nA malicious or compromised HTTP server can crash any client that composes the `decompress` interceptor with `dump` (or another response handler that throws), by returning a small compressed body that decompresses to more than the configured limit. The compressed bytes on the wire are tiny, so only the decompressed size matters. If the application keeps the process alive with a global uncaught-exception handler, the affected request instead hangs until the body timeout.\n\n## Patches\n\nUpgrade to undici 7.30.1 or 8.12.2.\n\n## Workarounds\n\nAvoid composing the `decompress` interceptor with a response handler that throws during response processing (such as `dump` with a `maxSize`) until upgrading.","summary":"undici's decompress interceptor passes decompressed data to downstream handlers from zlib callbacks without catching exceptions, so a handler that throws (such as dump with maxSize) becomes an uncaught exception. A malicious HTTP server can send a small compressed body that expands past the limit and terminate any client process that uses this combination.","severity":"high","cvss":7.5,"epss":0.0026,"exploited":false,"exploited_at":null,"products":[{"name":"undici","fixed":["7.30.1"],"affected":">= 7.15.0, < 7.30.1","ecosystem":"npm"},{"name":"undici","fixed":["8.12.2"],"affected":">= 8.0.0, < 8.12.2","ecosystem":"npm"},{"name":"nodejs undici","fixed":["7.30.1"],"affected":">= 7.15.0, < 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":["cwe-248","http-clients","node.js","package","undici"],"not_affected_if":["default-config","no-decompress-interceptor"],"how_to_check":"- Run `node -p \"require('undici/package.json').version\"` in the project and compare against the fixed versions.\n- Search lockfiles for `undici` and check whether code composes `interceptors.decompress` with `interceptors.dump` using `maxSize`.","fix":"- Upgrade `undici` to `7.30.1` (7.x line) or `8.12.2` (8.x line).\n- Until upgrading, avoid composing the `decompress` interceptor with a response handler that throws, such as `dump` with a `maxSize`.","status":"open","published_at":"2026-10-15T19:17:47+00:00","first_seen_at":"2026-10-27T19:04:56+00:00","triaged_at":"2026-10-27T19:05:56+00:00","updated_at":"2026-10-27T19:33:18+00:00","category":"package","confidence":0.85,"triage":{"at":"2026-10-27T19:05:56Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade `undici` to `7.30.1` (7.x line) or `8.12.2` (8.x line).\n- Until upgrading, avoid composing the `decompress` interceptor with a response handler that throws, such as `dump` with a `maxSize`.","reach":"internet","title":"undici: decompression interceptor lets a crafted response crash Node.js","impact":"low","summary":"undici's decompress interceptor passes decompressed data to downstream handlers from zlib callbacks without catching exceptions, so a handler that throws (such as dump with maxSize) becomes an uncaught exception. A malicious HTTP server can send a small compressed body that expands past the limit and terminate any client process that uses this combination.","category":"package","nicknames":[],"who_cares":["node.js","undici","http-clients"],"confidence":0.85,"needs_auth":"no","worst_case":"a remote server crashes the client Node.js process","analyst_note":"","how_to_check":"- Run `node -p \"require('undici/package.json').version\"` in the project and compare against the fixed versions.\n- Search lockfiles for `undici` and check whether code composes `interceptors.decompress` with `interceptors.dump` using `maxSize`.","needs_analyst":false,"not_affected_if":["default-config","no-decompress-interceptor"],"who_is_affected":"Only applications that use undici's decompress interceptor together with a response handler that throws during response processing, such as dump with a maxSize. Clients that call untrusted or third-party HTTP servers are the ones a malicious response can reach; apps that do not compose these interceptors can skip it.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"medium"},"cost_usd":0.000667,"input_tokens":3717,"output_tokens":590,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-2026':15A,23A '-248':32B '-87029':16A,24A '3pg8':20A '55wc':19A '7.30.1':265C '8.12.2':267C 'affect':253C 'aliv':244C 'anoth':205C 'applic':240C 'asynchron':146C 'avoid':269C 'becom':65B 'bodi':78B,215C,259C 'built':165C 'built-in':164C 'byte':226C 'callback':51B,110C,115C,150C 'catch':53B,112C 'client':35B,87B,196C 'combin':92B 'compos':198C,270C 'compress':77B,214C,225C 'compromis':190C 'configur':222C 'convert':121C 'crash':194C 'cve':14A,22A 'cwe':31B 'data':45B,101C 'decompress':12A,41B,44B,96C,99C,200C,217C,235C,272C 'denial':4A 'design':160C 'downstream':47B,104C,127C,155C 'dump':62B,167C,203C,285C 'engin':120C 'escap':177C 'event':109C 'exampl':162C 'exceed':174C 'except':9A,54B,68B,113C,181C,250C 'expand':80B 'failur':134C 'forward':98C 'ghsa':18A 'ghsa-55wc-3pg8-jfw6':17A 'global':247C 'handler':48B,57B,105C,128C,156C,207C,251C,277C 'hang':256C 'happen':145C 'http':34B,71B,191C 'http-client':33B 'impact':93C 'instead':255C 'interceptor':13A,42B,97C,168C,201C,273C 'jfw6':21A 'keep':241C 'limit':83B,223C 'malici':70B,188C 'matter':237C 'maxsiz':64B,176C,288C 'may':116C 'node.js':36B,185C 'nodejs':27A,29A 'packag':37B 'pass':43B 'past':81B 'patch':261C 'per':132C 'per-request':131C 'place':141C 'process':88B,186C,243C,282C 'protect':137C 'request':133C,254C 'respons':100C,173C,206C,276C,281C 'result':153C 'return':211C 'send':74B 'server':72B,192C 'servic':6A 'size':236C 'small':76B,213C 'stream':108C 'synchron':123C 'termin':85B,183C 'throw':59B,117C,124C,144C,158C,170C,209C,279C 'timeout':260C 'tini':231C 'uncaught':67B,180C,249C 'uncaught-except':248C 'undici':1A,25A,26A,28A,30A,38B,39B,94C,118C,264C 'unhandl':8A 'upgrad':262C,290C 'use':90B 'via':7A 'vulner':2A 'wire':229C 'without':52B,111C 'workaround':268C 'zlib':50B,107C,149C","nicknames":[],"mitigations":[],"who_affected":"Only applications that use undici's decompress interceptor together with a response handler that throws during response processing, such as dump with a maxSize. Clients that call untrusted or third-party HTTP servers are the ones a malicious response can reach; apps that do not compose these interceptors can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-15T19:17:47+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-55wc-3pg8-jfw6","url":"https://github.com/advisories/GHSA-55wc-3pg8-jfw6","severity":"medium","published_at":"2026-10-27T19:02:10+00:00","modified_at":"2026-10-27T19:02:12+00:00","first_seen_at":"2026-10-27T19:04:56+00:00","fetched_at":"2026-10-27T19:04:56+00:00","note":null},{"source":"nvd","external_id":"CVE-2026-87029","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-87029","severity":null,"published_at":"2026-10-15T19:17:47+00:00","modified_at":"2026-10-19T20:41:00+00:00","first_seen_at":"2026-10-27T19:33:18+00:00","fetched_at":"2026-10-27T19:33:18+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"}