SSRF via DNS-resolution gap in _validate_url_security (file download by URL) (CVE-2026-55096) | HOL Guard CVE

High · CVSS 7.1CVE-2026-55096

SSRF via DNS-resolution gap in _validate_url_security (file download by URL)

Answer in brief

CVE-2026-55096 records a High severity (CVSS 7.1) vulnerability in SSRF via DNS-resolution gap in _validate_url_security (file download by URL). The current sources do not mark it as known exploited. The current feed maps leshchenko1979/fast-mcp-telegram (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 Sep 28, 2026Updated Sep 28, 2026Source checked Sep 28, 2026First seen by HOL Sep 28, 2026Material review Sep 28, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.1
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 7.1. 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 leshchenko1979/fast-mcp-telegram (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
leshchenko1979/fast-mcp-telegramgeneric	<30.1	30.1

Recommended response

Check inventory. Check lockfiles and deployed manifests for leshchenko1979/fast-mcp-telegram.
Review the reported fix. Update leshchenko1979/fast-mcp-telegram to 30.1 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 28, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 28, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 28, 2026

Sources and claim methodology

Upstream source description

fast-mcp-telegram is a Telegram MCP Server. Prior to version 30.1, the send_message/send_message_to_phone MCP tools accept files as a list of http(s) URLs, which the server downloads and attaches to the outgoing Telegram message. Downloads are guarded by _validate_url_security, an SSRF denylist that checks the URL's literal hostname string but never resolves DNS. The fetch (httpx.AsyncClient.get) does its own resolution at request time. Consequently a hostname that resolves to a loopback / private / link-local address passes the guard and is fetched — even with the secure defaults block_private_ips=True and allow_http_urls=False. Because the fetched body is returned to the attacker as a Telegram file attachment, this is a full-read, exfiltrating SSRF, not blind. This issue has been patched in version 30.1.

Quoted source text, attributed separately from HOL analysis.