wasmtime: Numeric Truncation Error
CVE-2026-115889 is a critical-severity numeric truncation error vulnerability in wasmtime from Bytecodealliance, with a CVSS 3.1 base score of 9.9 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected wasmtime versions: < 36.0.19; >= 37.0.0, < 43.0.0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.45% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Check which version of wasmtime you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Bytecodealliance | wasmtime | < 36.0.19; >= 37.0.0, < 43.0.0 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (github.com).
Official description
Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Numeric Truncation Error
Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.
How developers prevent this class of flaw
- Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- github.com/bytecodealliance/wasmtime/commit/ba8f7d70caa1825b7f64fa75cd9d03f4a438dae0
- github.com/bytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0c9f11e56aa
- github.com/bytecodealliance/wasmtime/pull/12613
- github.com/bytecodealliance/wasmtime/pull/14818
- github.com/bytecodealliance/wasmtime/releases/tag/v36.0.19
- github.com/bytecodealliance/wasmtime/releases/tag/v43.0.0
Other vulnerabilities in wasmtime
- 7.9 High severity
- 9.9 Critical severity
- 7.9 High severity
- 9.9 Critical severity
Recent Numeric Truncation Error vulnerabilities
- 7.0 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 9.6 Critical severity
- 7.5 High severity
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