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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-55096
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-28 17:17:50 UTC
Updated2026-10-01 15:17:30 UTC
Descriptionfast-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.

Risk And Classification

Primary CVSS: v3.1 7.1 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

EPSS: 0.002050000 probability, percentile 0.094600000 (date 2026-10-04)

Problem Types: CWE-184 | CWE-918 | CWE-184 CWE-184: Incomplete List of Disallowed Inputs | CWE-918 CWE-918: Server-Side Request Forgery (SSRF)

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
3.1CNADECLARED7.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Leshchenko1979 Fast-mcp-telegram affected < 30.1 Not specified

References

ReferenceSourceLinkTags
github.com/leshchenko1979/fast-mcp-telegram/releases/tag/0.30.1 [email protected] github.com
github.com/leshchenko1979/fast-mcp-telegram/security/advisories/GHSA-xr7... 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/leshchenko1979/fast-mcp-telegram/commit/e6b3032cfc906e14f5b84... [email protected] github.com
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