{"id":"CVE-2026-121727","kind":"vulnerability","aliases":["CVE-2026-121727"],"related":[],"title":"Kore: integer underflow in HTTP body handling exhausts server memory","description":"Kore before 4.3.0 contains an integer underflow vulnerability in HTTP request body handling that allows unauthenticated attackers to bypass http_body_max by sending more body bytes than declared. Attackers can send oversized first segments over many concurrent POST, PUT or DELETE connections, wrapping content_length to grow buffers unbounded and exhaust worker memory.","summary":"Kore is a C web application framework whose HTTP request body handling has an integer underflow that lets unauthenticated clients bypass the http_body_max limit. An attacker can send oversized bodies over many concurrent POST, PUT or DELETE connections and exhaust worker memory.","severity":"high","cvss":8.7,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["c","http-servers","kore","runtime","self-hosted"],"not_affected_if":["kore-4.3.0-or-later","not-using-kore"],"how_to_check":"- Check the Kore version in use; affected versions are those before `4.3.0`.\n- Check whether `http_body_max` is set in the Kore configuration; the sources do not say whether the default configuration is affected.","fix":"- Kore: upgrade to `4.3.0` or later.","status":"open","published_at":"2026-11-03T23:17:36+00:00","first_seen_at":"2026-11-03T23:45:14+00:00","triaged_at":"2026-11-03T23:45:30+00:00","updated_at":"2026-11-03T23:45:30+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-11-03T23:45:30Z","model":"claude-haiku-5-5","output":{"fix":"- Kore: upgrade to `4.3.0` or later.","reach":"internet","title":"Kore: integer underflow in HTTP body handling exhausts server memory","impact":"medium","summary":"Kore is a C web application framework whose HTTP request body handling has an integer underflow that lets unauthenticated clients bypass the http_body_max limit. An attacker can send oversized bodies over many concurrent POST, PUT or DELETE connections and exhaust worker memory.","audience":"businesses","category":"runtime","nicknames":[],"who_cares":["kore","c","http-servers","self-hosted"],"confidence":0.6,"fix_status":"available","needs_auth":"no","worst_case":"Unauthenticated remote attackers exhaust worker memory, causing denial of service.","analyst_note":"","how_to_check":"- Check the Kore version in use; affected versions are those before `4.3.0`.\n- Check whether `http_body_max` is set in the Kore configuration; the sources do not say whether the default configuration is affected.","plain_action":"","needs_analyst":false,"not_affected_if":["kore-4.3.0-or-later","not-using-kore"],"who_is_affected":"Any service built on Kore before 4.3.0 that accepts HTTP POST, PUT or DELETE requests from the internet is exposed. Services that do not run Kore, or that sit behind a gateway enforcing body size limits, are less exposed; the sources do not say how much a gateway mitigates this.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000692,"input_tokens":4183,"output_tokens":548,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-121727':13A,16A '-2026':12A,15A '4.3.0':72C 'allow':84C 'applic':31B 'attack':53B,86C,99C 'bodi':6A,36B,49B,57B,81C,90C,95C 'buffer':118C 'bypass':46B,88C 'byte':96C 'c':17B,29B 'client':45B 'concurr':60B,107C 'connect':65B,112C 'contain':73C 'content':114C 'cve':11A,14A 'declar':98C 'delet':64B,111C 'exhaust':8A,67B,121C 'first':103C 'framework':32B 'grow':117C 'handl':7A,37B,82C 'host':25B 'http':5A,19B,34B,48B,79C,89C 'http-server':18B 'integ':2A,40B,75C 'kore':1A,21B,26B,70C 'length':115C 'let':43B 'limit':51B 'mani':59B,106C 'max':50B,91C 'memori':10A,69B,123C 'overs':56B,102C 'post':61B,108C 'put':62B,109C 'request':35B,80C 'runtim':22B 'segment':104C 'self':24B 'self-host':23B 'send':55B,93C,101C 'server':9A,20B 'unauthent':44B,85C 'unbound':119C 'underflow':3A,41B,76C 'vulner':77C 'web':30B 'whose':33B 'worker':68B,122C 'wrap':113C","nicknames":[],"mitigations":[],"who_affected":"Any service built on Kore before 4.3.0 that accepts HTTP POST, PUT or DELETE requests from the internet is exposed. Services that do not run Kore, or that sit behind a gateway enforcing body size limits, are less exposed; the sources do not say how much a gateway mitigates this.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["c","high","httpservers","kore","runtime","selfhosted"],"campaign_type":null,"first_public_at":"2026-11-03T23:17:36+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","cvss_by":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-121727","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-121727","severity":null,"published_at":"2026-11-03T23:17:36+00:00","modified_at":"2026-11-03T23:17:36+00:00","first_seen_at":"2026-11-03T23:45:14+00:00","fetched_at":"2026-11-03T23:45:14+00:00","note":null}],"documents":[{"id":61635,"url":"https://github.com/jorisvink/kore/commit/1ff3c0f6f7973dc7fc8bf38369790ef2d8079b3b","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":61636,"url":"https://www.vulncheck.com/advisories/kore-before-4.3.0-integer-underflow-memory-exhaustion-via-http-header-recv","title":"Third-party advisory: www.vulncheck.com","kind":"advisory","source":"nvd","publisher":"research","text":null,"published_at":null,"relation":"advisory","confidence":null,"note":"Third-party advisory: www.vulncheck.com"}],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}