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CVE-2026-121439— Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 HTTP Response Splitting via wasi-http

Quick assessment

Affected
bytecodealliance wasmtime
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Wasmtime 46.0.0 至 48.0.7 之前版本，以及 49.0.0 至 49.0.4 之前版本，在 wasi-http p3 组件中存在响应拆分漏洞。该漏洞允许 guest 设置未经验证的 Content-Length 头。恶意的 wasip3 guest 可将现有响应体拼接至新响应中，并设置错误的 Content-Length 值，从而实施响应拆分或注入攻击。

CVSS 5.3 · Medium
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I. Basic Information for CVE-2026-121439

Vulnerability Information
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Vulnerability Title
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 HTTP Response Splitting via wasi-http
Source: CVE Program / CVE List V5
Vulnerability Description
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 contains a response splitting vulnerability in wasi-http p3 that allows guests to set unvalidated content-length headers. Malicious wasip3 guests can splice an existing body into a new response with an incorrect content-length to perform response splitting or injection attacks.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
bytecodealliance wasmtime 46.0.0 ~ 48.0.7 -

II. Public POCs for CVE-2026-121439

# POC Description Source Link Shenlong Link
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III. Intelligence Information for CVE-2026-121439

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Other References for CVE-2026-121439 (2)

Same Patch Batch · bytecodealliance · 2026-11-03 · 3 CVEs total

CVE-2026-121440 3.7 LOW Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 Forwarded Trailers Header Filter By
CVE-2026-121441 3.7 LOW Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 wasi-http Request

IV. Related Vulnerabilities

Same product: wasmtime
Same vendor: bytecodealliance
Same weakness: CWE-444