vulnerability / NVI-00012905 / Revision 3
Wasmtime: Preemption and traps during bulk operations enable breaking internal VM state
GitHub lists this reviewed advisory for wasmtime, wasmtime. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
2 LOW (4.0)
security-advisories@github.com severity; no combined Null risk score.
0.276%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.20086. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
wasmtime
source listed>= 46.0.0, < 46.0.2
### Impact Wasmtime's implementation of bulk-data-transfer WebAssembly instructions, such as `memory.copy`, contains a vulnerability when a preemption via epochs or fuel is combined with altering the store's state or cancelling a computation. To prevent these operations from taking too long Wasmtime injects fuel/epoch checks during these operations, but this enables embedders, and possible WebAssembly, to witness intermediate state in the middle of the operation. Examples of this include: * When a non-nullable WebAssembly table is grown the new elements initially start as null and are filled in as part of a loop with preemption checks. If this computation is then cancelled this left the table in a grown-but-uninitialized state where subsequent usage via WebAssembly could possibly segfault. Loads from this table are assumed to not be null due to its type, but the runtime implementation was exposed through this cancellation at a preemption point. * Embedders could mutate the store during an epoch callback, such as growing a WebAssembly linear memory. During a bulk `memory.copy` operation, however, the pointers being copied to/from weren't recomputed between preemption points. This
wasmtime
source listed>= 47.0.0, < 47.0.3
### Impact Wasmtime's implementation of bulk-data-transfer WebAssembly instructions, such as `memory.copy`, contains a vulnerability when a preemption via epochs or fuel is combined with altering the store's state or cancelling a computation. To prevent these operations from taking too long Wasmtime injects fuel/epoch checks during these operations, but this enables embedders, and possible WebAssembly, to witness intermediate state in the middle of the operation. Examples of this include: * When a non-nullable WebAssembly table is grown the new elements initially start as null and are filled in as part of a loop with preemption checks. If this computation is then cancelled this left the table in a grown-but-uninitialized state where subsequent usage via WebAssembly could possibly segfault. Loads from this table are assumed to not be null due to its type, but the runtime implementation was exposed through this cancellation at a preemption point. * Embedders could mutate the store during an epoch callback, such as growing a WebAssembly linear memory. During a bulk `memory.copy` operation, however, the pointers being copied to/from weren't recomputed between preemption points. This
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-2hw9-mc66-jc2q ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-104855 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-104855 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Source facts changed; compare the preserved prior revision.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.