CVE-2026-126409bytecodealliance wasmtime type confusion
CVE-2026-126409 is a type confusion in bytecodealliance wasmtime, rated low (1.8 on CVSS 4.0).
Why this priority: Low severity, with no exploitation signal.
Published · Updated · NVD status: Deferred
What it is
Memory holding one type of object is treated as another, often a route to code execution in browsers and script engines.
How it is reached
An attacker can exploit it over the network, with an administrator account, but someone has to act first, such as opening a file or following a link. Success also depends on conditions the attacker does not fully control.
What an attacker gains
The direct impact is limited: partial access to data or a partial outage. In practice, this kind of flaw lets an attacker crash the process, read memory, or in the worst case run code.
Is it being exploited?
There is no public report of exploitation yet. EPSS estimates a 0.27% chance of exploitation activity in the next 30 days, higher than 20% of scored CVEs.
What to do
- Upgrade bytecodealliance wasmtime to a fixed version for your release line (48.0.8, 49.0.5, 50.0.1).
- Until it is patched, review who holds accounts that can reach it.
- Warn the people who use it, and filter files and links on the way in.
Description from NVD
Wasmtime 47.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 contains a cross-engine type confusion vulnerability because StructType::with_finality_and_supertype does not validate that the supplied supertype belongs to the same Engine. Embedders using multiple engines that create a GC struct type with another engine's supertype can trigger runtime panics or GC heap corruption, causing denial of service; guest WebAssembly cannot trigger it.
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Native code: operating systems, browsers and firmware. The flaw sits wherever native code reads untrusted data.
- Network appliances and media or file parsers. The flaw sits wherever native code reads untrusted data.
Trust boundaries in play
- Authenticated network access. An account is needed, so exposure follows who can sign in: customers, partners or staff.
- People who open files and links. Mail, chat and browsers are the delivery path.
- Wherever native code reads untrusted data. An attacker who crosses it can crash the process, read memory, or in the worst case run code.
Questions to answer about your own systems
- Where does bytecodealliance wasmtime run in your systems, and at which version?
- Which of those instances can be reached from the internet or partner networks?
- What can it reach once compromised: which data stores, secrets and services?
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.