{"id":"CVE-2026-126407","kind":"vulnerability","aliases":["CVE-2026-126407"],"related":[],"title":"Wasmtime: untracked borrowed resources let a guest exhaust host memory","description":"Wasmtime before 36.0.20, 37.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 allocates untracked host memory when a component receives a borrow of a resource it defines itself, bypassing the per-store handle limit. A malicious guest component can repeatedly transfer such borrowed resources to consume arbitrary host memory, causing denial of service.","summary":"Wasmtime allocates host memory for borrowed resources without counting them against the per-store handle limit. A malicious guest component can repeat these transfers to consume arbitrary host memory and cause a denial of service.","severity":"medium","cvss":5.9,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["runtime","self-hosted","wasmtime","webassembly"],"not_affected_if":["no-component-model","trusted-guests-only"],"how_to_check":"- Check the Wasmtime version your application links against, for example `wasmtime --version` or the crate version in `Cargo.lock`.\n- Confirm whether you run untrusted WebAssembly component guests in your process.","fix":"- Wasmtime `36.0.20`\n- Wasmtime `48.0.8`\n- Wasmtime `49.0.5`\n- Wasmtime `50.0.1`","status":"open","published_at":"2026-11-13T10:17:45+00:00","first_seen_at":"2026-11-13T10:47:19+00:00","triaged_at":"2026-11-13T10:56:44+00:00","updated_at":"2026-11-13T10:56:44+00:00","category":"runtime","confidence":0.6,"triage":{"at":"2026-11-13T10:56:44Z","model":"claude-haiku-5-5","output":{"fix":"- Wasmtime `36.0.20`\n- Wasmtime `48.0.8`\n- Wasmtime `49.0.5`\n- Wasmtime `50.0.1`","reach":"unknown","title":"Wasmtime: untracked borrowed resources let a guest exhaust host memory","impact":"low","summary":"Wasmtime allocates host memory for borrowed resources without counting them against the per-store handle limit. A malicious guest component can repeat these transfers to consume arbitrary host memory and cause a denial of service.","audience":"businesses","category":"runtime","nicknames":[],"who_cares":["wasmtime","webassembly","self-hosted"],"confidence":0.6,"fix_status":"available","needs_auth":"unknown","worst_case":"Malicious guest exhausts host memory, causing denial of service","analyst_note":"","how_to_check":"- Check the Wasmtime version your application links against, for example `wasmtime --version` or the crate version in `Cargo.lock`.\n- Confirm whether you run untrusted WebAssembly component guests in your process.","plain_action":"","product_name":"","needs_analyst":false,"not_affected_if":["trusted-guests-only","no-component-model"],"who_is_affected":"Applications that embed Wasmtime and run untrusted WebAssembly component guests are exposed, because a guest can trigger the unbounded host allocation. Systems that run only trusted components or do not use the component model with resource borrows can skip it.","user_interaction":"no","product_ecosystem":"","needs_special_setup":"unknown","severity_if_unknown":"medium"},"cost_usd":0.000739,"input_tokens":4665,"output_tokens":544,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-126407':13A,16A '-2026':12A,15A '36.0.20':61C '37.0.0':62C '48.0.8':64C '49.0.0':65C '49.0.5':67C '50.0.0':69C '50.0.1':71C 'alloc':24B,72C 'arbitrari':50B,107C 'borrow':3A,28B,81C,103C 'bypass':88C 'caus':54B,110C 'compon':43B,78C,98C 'consum':49B,106C 'count':31B 'cve':11A,14A 'defin':86C 'denial':56B,111C 'exhaust':8A 'guest':7A,42B,97C 'handl':38B,93C 'host':9A,20B,25B,51B,74C,108C 'let':5A 'limit':39B,94C 'malici':41B,96C 'memori':10A,26B,52B,75C,109C 'per':36B,91C 'per-stor':35B,90C 'receiv':79C 'repeat':45B,100C 'resourc':4A,29B,84C,104C 'runtim':17B 'self':19B 'self-host':18B 'servic':58B,113C 'store':37B,92C 'transfer':47B,101C 'untrack':2A,73C 'wasmtim':1A,21B,23B,59C 'webassembl':22B 'without':30B","nicknames":[],"mitigations":[],"who_affected":"Applications that embed Wasmtime and run untrusted WebAssembly component guests are exposed, because a guest can trigger the unbounded host allocation. Systems that run only trusted components or do not use the component model with resource borrows can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["medium","runtime","selfhosted","wasmtime","webassembly"],"campaign_type":null,"search_a":"'-126407':13A,16A '-2026':12A,15A 'borrow':3A 'cve':11A,14A 'exhaust':8A 'guest':7A 'host':9A 'let':5A 'memori':10A 'resourc':4A 'untrack':2A 'wasmtim':1A","search_b":"'alloc':24B 'arbitrari':50B 'borrow':28B 'caus':54B 'compon':43B 'consum':49B 'count':31B 'denial':56B 'guest':42B 'handl':38B 'host':20B,25B,51B 'limit':39B 'malici':41B 'memori':26B,52B 'per':36B 'per-stor':35B 'repeat':45B 'resourc':29B 'runtim':17B 'self':19B 'self-host':18B 'servic':58B 'store':37B 'transfer':47B 'wasmtim':21B,23B 'webassembl':22B 'without':30B","search_c":"'36.0.20':61C '37.0.0':62C '48.0.8':64C '49.0.0':65C '49.0.5':67C '50.0.0':69C '50.0.1':71C 'alloc':72C 'arbitrari':107C 'borrow':81C,103C 'bypass':88C 'caus':110C 'compon':78C,98C 'consum':106C 'defin':86C 'denial':111C 'guest':97C 'handl':93C 'host':74C,108C 'limit':94C 'malici':96C 'memori':75C,109C 'per':91C 'per-stor':90C 'receiv':79C 'repeat':100C 'resourc':84C,104C 'servic':113C 'store':92C 'transfer':101C 'untrack':73C 'wasmtim':59C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-10-29T19:06:21+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/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-2026-126407","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-126407","severity":null,"published_at":"2026-11-13T10:17:45+00:00","modified_at":"2026-11-13T10:17:45+00:00","first_seen_at":"2026-11-13T10:47:19+00:00","fetched_at":"2026-11-13T10:47:19+00:00","note":null}],"documents":[{"id":145057,"url":"https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-6fr9-xmw9-5352","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-10-29T19:06:21+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"},{"id":145058,"url":"https://www.vulncheck.com/advisories/wasmtime-before-36.0.20-denial-of-service-via-borrowed-resource-transfer","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"}],"disclosures":[],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}