CVE-2026-121439

Medium

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.

SeverityMedium

CVSS5.3

Exploit probability—

ProductBytecodealliance Wasmtime

PublishedNov 3, 2026

First seenNov 4, 2026

Weakness typeCWE-444CWE-444

How to fix

Update

bytecodealliance wasmtime48.0.7, 49.0.4 or later

Vendor advisories

github.com/bytecodealliance/wasmtime/security/advisories/GHSA-9prg-84vf-g5fc

Affected products

Product	Affected versions	Fixed in
bytecodealliance wasmtime	46.0.0 ≤ v < 48.0.7, 49.0.0 ≤ v < 49.0.4	48.0.7, 49.0.4

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