CVE-2026-58483: mcp-searxng: Unbounded Response Body Read Bypasses URL Size Limit in `web_url_read`
mcp-searxng is a Model Context Protocol server that gives AI assistants web search and URL-reading capabilities through SearXNG. Prior to 1.7.1, weburlread in src/index.ts passes a caller-supplied URL to readUrlContent() in src/url-reader.ts, where checkContentLength() treats a missing Content-Length header as an inconclusive preflight and the normal and error paths then consume the complete body with response.text(). A server that omits Content-Length can therefore bypass URLREADMAXCONTENTLENGTHBYTES and force unbounded memory use. The resulting string is also processed by NodeHtmlMarkdown.translate(), increasing CPU consumption and allowing an unauthenticated HTTP client to cause denial of service. This issue is fixed in version 1.7.1.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
mcp-searxngto a version that resolves this vulnerability.Fixed in 1.7.1
Event History
Frequently Asked Questions
Which deployments are exposed to this denial-of-service issue?
mcp-searxng versions prior to 1.7.1 are affected where an unauthenticated HTTP client can invoke the web_url_read capability. The issue can be triggered by directing the server to a response that omits the Content-Length header.
What does an attacker need to do to exploit this?
An attacker needs network access to the HTTP interface and does not need authentication or user interaction. They supply a URL whose server returns a body without Content-Length, causing mcp-searxng to read the complete response and process it as HTML-to-Markdown content.
Is the configured URL response-size limit sufficient protection?
No. Before 1.7.1, URL_READ_MAX_CONTENT_LENGTH_BYTES can be bypassed when the upstream response omits Content-Length, because the implementation treats the absent header as inconclusive and reads the full body.
What is the remediation?
Upgrade mcp-searxng to version 1.7.1. This version fixes the unbounded response-body read in web_url_read.