{"id":"CVE-2026-115889","kind":"vulnerability","aliases":["CVE-2026-115889","GHSA-897f-g5gm-fmxm"],"related":[],"title":"Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation","description":"## Summary\n\nIn Wasmtime prior to v43, the Cranelift compiler backend bit-packs its SSA value indices in a way that can result in silent overflow in release builds, and result in incorrect value references in the IR resulting in arbitrary miscompilation. A very large Wasm function body, or one that is specially crafted to use many SSA values, can use this to force type-confusion or other arbitrary side-effects and escape the sandbox.\n\nCranelift was changed in Wasmtime v43 to use a full `u32` index, with checks if that limit is exceeded, and so is no longer susceptible to this bug.\n\n## Impact\n\nA Wasmtime engine with default settings (using the Cranelift backend) on any architecture/platform could experience a sandbox escape from a specially-crafted Wasm module.\n\n## Patches\n\nWasmtime v36.0.19 has been released which fixes this issue.","summary":"Wasmtime's Cranelift compiler packs SSA value indices into bits, so large or crafted WebAssembly functions can overflow silently in release builds and produce incorrect code. The advisory says an attacker can use a specially crafted Wasm module to escape the sandbox.","severity":"critical","cvss":9.9,"epss":0.00663,"exploited":false,"exploited_at":null,"products":[{"name":"wasmtime","fixed":["36.0.19"],"affected":"< 36.0.19","ecosystem":"cargo"},{"name":"wasmtime","fixed":["43.0.0"],"affected":">= 37.0.0, < 43.0.0","ecosystem":"cargo"}],"ecosystems":["cargo"],"tags":["cwe-197","cwe-843","package","rust","wasm-runtime","wasmtime"],"not_affected_if":["wasmtime-43-or-later","wasmtime-below-36-not-used"],"how_to_check":"Run `cargo tree -i wasmtime` or check Cargo.lock for wasmtime versions below 36.0.19 or in the 37.0.0 to below 43.0.0 range.","fix":"Upgrade wasmtime to 36.0.19 if on the 36.x line, or to 43.0.0 if on the 37.x to 42.x line.","status":"open","published_at":"2026-10-23T22:02:20+00:00","first_seen_at":"2026-10-23T22:05:18+00:00","triaged_at":"2026-10-23T22:06:30+00:00","updated_at":"2026-10-25T12:38:49+00:00","category":"package","confidence":0.8,"triage":{"at":"2026-10-23T22:06:30Z","model":"claude-haiku-5-5","output":{"fix":"Upgrade wasmtime to 36.0.19 if on the 36.x line, or to 43.0.0 if on the 37.x to 42.x line.\nunknown","reach":"internet","impact":"high","summary":"Wasmtime's Cranelift compiler packs SSA value indices into bits, so large or crafted WebAssembly functions can overflow silently in release builds and produce incorrect code. The advisory says an attacker can use a specially crafted Wasm module to escape the sandbox.","category":"package","who_cares":["wasmtime","rust","wasm-runtime"],"confidence":0.8,"needs_auth":"no","worst_case":"Attacker-supplied Wasm module escapes sandbox and runs arbitrary code in host.","analyst_note":"Confirm the exact Cargo versions affected and whether the 36.x branch fix at 36.0.19 covers all sub-variants; check https://github.com/advisories/GHSA-897f-g5gm-fmxm for detail.","how_to_check":"Run `cargo tree -i wasmtime` or check Cargo.lock for wasmtime versions below 36.0.19 or in the 37.0.0 to below 43.0.0 range.\nunknown\nunknown","needs_analyst":true,"not_affected_if":["wasmtime-below-36-not-used","wasmtime-43-or-later"],"user_interaction":"no","needs_special_setup":"no","severity_if_unknown":"critical"},"cost_usd":0.000559,"input_tokens":3074,"output_tokens":503,"severity_before":"critical"},"analyst_status":null,"analyst_note":null,"search":"'-115889':15A,23A '-197':27B '-2026':14A,22A '-843':29B '897f':18A 'advisori':63B 'arbitrari':118C,147C 'architecture/platform':196C 'attack':66B 'backend':87C,193C 'bit':3A,45B,89C 'bit-pack':2A,88C 'bodi':125C 'bug':182C 'build':57B,106C 'caus':8A 'chang':157C 'check':168C 'code':61B 'compil':7A,39B,86C 'confus':144C 'could':197C 'craft':49B,71B,131C,206C 'cranelift':6A,38B,85C,155C,192C 'cve':13A,21A 'cwe':26B,28B 'default':188C 'effect':150C 'engin':186C 'escap':75B,152C,201C 'exceed':173C 'experi':198C 'fix':216C 'fmxm':20A 'forc':141C 'full':164C 'function':51B,124C 'g5gm':19A 'ghsa':17A 'ghsa-897f-g5gm-fmxm':16A 'impact':183C 'incorrect':60B,110C 'index':166C 'indic':43B,94C 'ir':115C 'issu':218C 'larg':47B,122C 'limit':171C 'longer':178C 'mani':134C 'miscompil':12A,119C 'modul':73B,208C 'one':127C 'overflow':10A,53B,103C 'pack':4A,40B,90C 'packag':30B 'patch':209C 'prior':81C 'produc':59B 'refer':112C 'releas':56B,105C,214C 'result':100C,108C,116C 'runtim':34B 'rust':31B 'sandbox':77B,154C,200C 'say':64B 'set':189C 'side':149C 'side-effect':148C 'silent':9A,54B,102C 'special':70B,130C,205C 'specially-craft':204C 'ssa':41B,92C,135C 'summari':78C 'suscept':179C 'type':143C 'type-confus':142C 'u32':165C 'use':68B,133C,138C,162C,190C 'v36.0.19':211C 'v43':83C,160C 'valu':42B,93C,111C,136C 'wasm':33B,72B,123C,207C 'wasm-runtim':32B 'wasmtim':1A,35B,36B,80C,159C,185C,210C 'wasmtime':24A,25A 'way':97C 'webassembl':50B","nicknames":[],"mitigations":[],"who_affected":null,"tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T22:02:20+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","cvss_by":"GitHub","poc_count":0,"sources":[{"source":"ghsa","external_id":"GHSA-897f-g5gm-fmxm","url":"https://github.com/advisories/GHSA-897f-g5gm-fmxm","severity":"critical","published_at":"2026-10-23T22:02:20+00:00","modified_at":"2026-10-23T22:02:21+00:00","first_seen_at":"2026-10-23T22:05:18+00:00","fetched_at":"2026-10-23T22:05:18+00:00","note":null},{"source":"nvd","external_id":"CVE-2026-115889","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-115889","severity":null,"published_at":"2026-10-23T22:16:58+00:00","modified_at":"2026-10-23T22:16:58+00:00","first_seen_at":"2026-10-23T23:44:51+00:00","fetched_at":"2026-10-23T23:44:52+00:00","note":null},{"source":"epss","external_id":"CVE-2026-115889","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-115889","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-25T12:38:49+00:00","fetched_at":"2026-10-25T12:38:49+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"}