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    CVE-2026-121439

    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.

    Published:Nov 3, 2026
    Last Modified:Nov 3, 2026
    EPS:Nov 3, 2026
    EPSS Score:
    CVSS Score:5.3

    Affected Products

    Vendor
    Bytecodealliance
    Product
    Wasmtime

    Exploits

    No exploit reference

    Common Attack Pattern Enumeration and Classification (CAPEC)

    CAPEC-273 HTTP Response Smuggling
    CAPEC-33 HTTP Request Smuggling

    Related CVEs

    CVE-2026-121441 (CVSS 6.3) — Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 contains a request smuggling vulnerabi…
    CVE-2026-121440 (CVSS 6.3) — Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 fails to check forwarded trailers against the WasiHttpH…
    CVE-2026-119142 (CVSS 5.9) — Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a denial of service vulnerability where droppi…
    CVE-2026-119143 (CVSS 5.9) — Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a denial of service vulnerability that allows …
    CVE-2026-119141 (CVSS 6.9) — Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a denial of service vulnerability that allows …
    CVE-2026-119140 (CVSS 5.9) — Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a denial of service vulnerability that allows …
    CVE-2026-119139 (CVSS 5.9) — Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a leftover assertion in component::Func::call …
    CVE-2026-119138 (CVSS 5.9) — Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a denial of service vulnerability that allows …
    CVE-2026-119137 (CVSS 6.9) — Wasmtime 42.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a stack overflow vulnerability that allows gue…
    CVE-2026-119136 (CVSS 5.9) — Wasmtime 42.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains insufficient checks in Store when mixing async…

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High