Medium · CVSS 6.3CVE-2026-126406

Wasmtime before 36.0.20 HTTP Request Smuggling via wasi-http p2 Content-LengthCVE-2026-126406

Answer in brief

CVE-2026-126406 records a Medium severity (CVSS 6.3) vulnerability in Wasmtime before 36.0.20 HTTP Request Smuggling via wasi-http p2 Content-Length. The current sources do not mark it as known exploited. The current feed maps bytecodealliance/wasmtime (generic), bytecodealliance/wasmtime (generic), bytecodealliance/wasmtime (generic), bytecodealliance/wasmtime (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Nov 13, 2026Updated Nov 13, 2026Source checked Nov 13, 2026First seen by HOL Nov 13, 2026Material review Nov 13, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.3
Exploitation: Not marked as known exploited
Affected software: 4 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 6.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps bytecodealliance/wasmtime (generic), bytecodealliance/wasmtime (generic), bytecodealliance/wasmtime (generic), bytecodealliance/wasmtime (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
bytecodealliance/wasmtimegeneric	>=0 <36.0.20	36.0.20
bytecodealliance/wasmtimegeneric	>=37.0.0 <48.0.8	48.0.8
bytecodealliance/wasmtimegeneric	>=49.0.0 <49.0.5	49.0.5
bytecodealliance/wasmtimegeneric	>=50.0.0 <50.0.1	50.0.1

Recommended response

Check inventory. Check lockfiles and deployed manifests for bytecodealliance/wasmtime, bytecodealliance/wasmtime, bytecodealliance/wasmtime.
Review the reported fix. Update bytecodealliance/wasmtime to 36.0.20; bytecodealliance/wasmtime to 48.0.8; bytecodealliance/wasmtime to 49.0.5; bytecodealliance/wasmtime to 50.0.1 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Nov 13, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Nov 13, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Nov 13, 2026

Sources and claim methodology

Upstream source description

The wasmtime-wasi-http p2 implementation in Wasmtime before 36.0.20, 37.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 can send conflicting content-length headers, or ones not matching the body, in outgoing requests. A guest that reuses a received response's headers resource to send a bodyless request can enable request smuggling against non-compliant servers, potentially bypassing embedder destination access controls.

Quoted source text, attributed separately from HOL analysis.

Affected scope and exposure questions

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
bytecodealliance/wasmtimegeneric	>=0 <36.0.20	36.0.20
bytecodealliance/wasmtimegeneric	>=37.0.0 <48.0.8	48.0.8
bytecodealliance/wasmtimegeneric	>=49.0.0 <49.0.5	49.0.5
bytecodealliance/wasmtimegeneric	>=50.0.0 <50.0.1	50.0.1

Recommended response

Check inventory. Check lockfiles and deployed manifests for bytecodealliance/wasmtime, bytecodealliance/wasmtime, bytecodealliance/wasmtime.

Review the reported fix. Update bytecodealliance/wasmtime to 36.0.20; bytecodealliance/wasmtime to 48.0.8; bytecodealliance/wasmtime to 49.0.5; bytecodealliance/wasmtime to 50.0.1 if you use the affected versions. Test the change in a non-production environment first.

Sources and claim methodology

Upstream source description

Quoted source text, attributed separately from HOL analysis.