Is CVE-2026-121439 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-121439?

CVE-2026-121439 has a CVSS v3 severity of MEDIUM (5.3).

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CVE-2026-121439

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.