High · CVSS 8.8CVE-2026-42559GHSA-89VP-X53W-74FX

DNS rebinding and cross-origin CSRF in dynoxide's MCP HTTP transportCVE-2026-42559

Answer in brief

CVE-2026-42559 records a High severity (CVSS 8.8) vulnerability in DNS rebinding and cross-origin CSRF in dynoxide's MCP HTTP transport. The current sources do not mark it as known exploited. The current feed maps dynoxide-rs (crates.io). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

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

Published May 12, 2026Updated Oct 12, 2026Source checked Oct 12, 2026First seen by HOL Oct 12, 2026Material review Oct 12, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.8
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 8.8. 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 dynoxide-rs (crates.io). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
dynoxide-rscrates.io	>=0.9.3 <0.9.13	0.9.13

Recommended response

Check inventory. Check lockfiles and deployed manifests for dynoxide-rs.
Review the reported fix. Update dynoxide-rs to 0.9.13 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
May 12, 2026
Evidence: source:osv:source_dates:source-dates:record
Source modified
Oct 12, 2026
Evidence: source:osv:source_dates:source-dates:record
First seen by HOL
Oct 12, 2026

Sources and claim methodology

Upstream source description

dynoxide's MCP HTTP transport was vulnerable to DNS rebinding via its transitive `rmcp` dependency, plus a related cross-origin CSRF gap. A malicious web page could make the user's browser send requests to a local `dynoxide mcp --http` or `dynoxide serve --mcp` server with a non-loopback `Host` header, which the server would then process. The Host check alone did not close a related cross-origin CSRF vector: a page could `fetch` the loopback endpoint with `mode: 'no-cors'`, and the Host header would match while the Origin header went unchecked. Affected MCP write tools include `put_item`, `update_item`, `delete_item`, `create_table`, and `batch_write_item`. The stdio transport (`dynoxide mcp` without `--http`) is not affected. ## Patches dynoxide 0.9.13 closes both vectors: - Upgrades `rmcp` from 1.1.1 to 1.6.0 (which ships a default Host-header allowlist). - Sets explicit `allowed_hosts` and `allowed_origins` on `StreamableHttpServerConfig`.

Quoted source text, attributed separately from HOL analysis.