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CVE-2022-39393

HIGH
Published 2022-11-10T00:00:00.000Z
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CVSS Score

V3.1
8.6
/10
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
Base Score Metrics
Exploitability: N/A Impact: N/A

EPSS Score

v2025.03.14
0.001
probability
of exploitation in the wild

There is a 0.1% chance that this vulnerability will be exploited in the wild within the next 30 days.

Updated: 2025-06-25
Exploit Probability
Percentile: 0.276
Higher than 27.6% of all CVEs

Attack Vector Metrics

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED

Impact Metrics

Confidentiality
HIGH
Integrity
NONE
Availability
NONE

Description

Wasmtime is a standalone runtime for WebAssembly. Prior to versions 2.0.2 and 1.0.2, there is a bug in Wasmtime's implementation of its pooling instance allocator where when a linear memory is reused for another instance the initial heap snapshot of the prior instance can be visible, erroneously to the next instance. This bug has been patched and users should upgrade to Wasmtime 2.0.2 and 1.0.2. Other mitigations include disabling the pooling allocator and disabling the `memory-init-cow`.

Available Exploits

No exploits available for this CVE.

Related News

No news articles found for this CVE.

Affected Products

GitHub Security Advisories

Community-driven vulnerability intelligence from GitHub

✓ GitHub Reviewed HIGH

Wasmtime may have data leakage between instances in the pooling allocator

GHSA-wh6w-3828-g9qf

Advisory Details

### Impact There is a bug in Wasmtime's implementation of it's pooling instance allocator where when a linear memory is reused for another instance the initial heap snapshot of the prior instance can be visible, erroneously to the next instance. The pooling instance allocator in Wasmtime works by preallocating virtual memory for a fixed number of instances to reside in and then new instantiations pick a slot to use. Most conventional modules additionally have an initial copy-on-write "heap image" which is mapped in Wasmtime into the linear memory slot. When a heap slot is deallocated Wasmtime resets all of its contents back to the initial state but it does not unmap the image in case the next instance is an instantiation of the same module. The bug in Wasmtime occurs when a slot in the pooling allocator previously was used for a module with a heap image, meaning that its current state of memory contains the initial heap contents of that module. If the next instantiation within that slot does not itself contain a heap image then Wasmtime would leave the old heap image in place erroneously and continue with instantiation. This means that instantiations of modules without a heap image can see the initial heap image of the prior instantiation within that slot. Heap images in Wasmtime are created by precomputing WebAssembly `data` segments into one large mapping to be placed into linear memory at a particular offset. Most modules produced by toolchains today will have a heap image and an initialization snapshot. Creating a module without a heap image would require a hand-crafted `*.wat` file or a specially crafted source program. This consequence means that this bug is highly unlikely to be accidentally triggered and would otherwise require an intentional trigger with a hand-crafted module. One important part of this vulnerability is Wasmtime is highly likely to segfault when the slot is reused again with a module that itself has an initialization image. For example if module A has a heap initialization image and module B does not have a heap initialization image, then the following sequence of events could happen if they all are instantiated into the same instance slot: * Module A is instantiated, and then deallocated. This leaves A's heap image in place, reset to its initial contents. * Module B is instantiated and erroneously can see the initial heap contents of A. Module B is then deallocated and the entire heap is unmapped and reset back to zero. * Module A is instantiated again, but the state tracking the slot did not account for module B so it thinks the module image is still mapped and proceeds with instantiation. Any action on A's part to access linear memory will then trap and if the host accesses A's memory it will segfault because the data that's supposed to be mapped is all unmapped. Adding this all together this means that in practice modules must be deliberately crafted to not have an initial heap image to view the contents of a prior image. If this module is instantiated though then when the slot is reused the next, likely image-using, module will believe its memory is mapped when it isn't, causing the host to segfault on unmapped memory it believed was mapped. ### Patches This bug has been patched and users should upgrade to Wasmtime 2.0.2. ### Workarounds Trigging this bug requires the pooling allocator to be configured and for copy-on-write heap images to also be enabled. Pooling allocation is not enabled by default but copy-on-write heap images are. Mitigations for this bug include: * Disabling the pooling allocator - note that pooling allocation is not enabled by default in Wasmtime * Disabling the `memory-init-cow` feature or with [`Config::memory_init_cow`](https://docs.rs/wasmtime/2.0.1/wasmtime/struct.Config.html#method.memory_init_cow) ### References * [`Config::allocation_strategy`](https://docs.rs/wasmtime/2.0.1/wasmtime/struct.Config.html#method.allocation_strategy) - configuration required to enable the pooling allocator. * [`Config::memory_init_cow`](https://docs.rs/wasmtime/2.0.1/wasmtime/struct.Config.html#method.memory_init_cow) - configuration required to enable or disable copy-on-write (this is enabled by default). * [Mailing list announcement](https://groups.google.com/a/bytecodealliance.org/g/sec-announce/c/c1HBDDJwNPA) * [Patch for `release-2.0.0` branch](https://github.com/bytecodealliance/wasmtime/commit/2614f2e9d2d36805ead8a8da0fa0c6e0d9e428a0) * [Patch for `main`](https://github.com/bytecodealliance/wasmtime/commit/3535acbf3be032ef1ba0b469b8ab92538a8a18a6) ### For more information If you have any questions or comments about this advisory: * Reach out to us on [the Bytecode Alliance Zulip chat](https://bytecodealliance.zulipchat.com/#narrow/stream/217126-wasmtime) * Open an issue in [the bytecodealliance/wasmtime repository](https://github.com/bytecodealliance/wasmtime/)

Affected Packages

crates.io wasmtime
ECOSYSTEM: ≥2.0.0 <2.0.2
crates.io wasmtime
ECOSYSTEM: ≥0 <1.0.2

CVSS Scoring

CVSS Score

7.5

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Advisory provided by GitHub Security Advisory Database. Published: November 10, 2022, Modified: May 2, 2025

References

Published: 2022-11-10T00:00:00.000Z
Last Modified: 2025-05-02T12:51:28.525Z
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