SSRF via DNS-resolution gap in _validate_url_security (file download by URL)
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-55096
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 3 Nov 2026, 11:01 UTC · Revision 1
Source evidence
SSRF via DNS-resolution gap in _validate_url_security (file download by URL)
core-osv · Original sourcePublished 28 Sept 2026, 16:38 UTC
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.
osv:CVE-2026-55096
Complete source record
{
"id": "59b8f274992f63b68b68bf087563dc7a8a9987fab6515b4ba69f4b2867128715",
"url": "https://osv.dev/vulnerability/CVE-2026-55096",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "SSRF via DNS-resolution gap in _validate_url_security (file download by URL)",
"summary": "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.",
"evidence": "osv:CVE-2026-55096",
"products": [],
"severity": "high",
"structured": {
"id": "CVE-2026-55096",
"aliases": [
"CVE-2026-55096",
"GHSA-xr72-j7vj-vp7g"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/leshchenko1979/fast-mcp-telegram",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "e6b3032cfc906e14f5b84f2c2b8ec378eb457e57"
},
{
"fixed": "efba6fa01232dacb1480bbcfdf1eeb2cf2c09723"
}
],
"database_specific": {
"extracted_events": [
{
"range": [
{
"fixed": "e6b3032cfc906e14f5b84f2c2b8ec378eb457e57"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "efba6fa01232dacb1480bbcfdf1eeb2cf2c09723"
}
],
"source": "REFERENCES_TAG",
"original_tag": "0.30.1"
}
]
}
}
],
"versions": [
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],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55096.json"
}
}
],
"modified": "2026-10-28T02:30:28.004549768Z",
"provider": "osv",
"references": [
"https://github.com/leshchenko1979/fast-mcp-telegram/releases/tag/0.30.1",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55096.json",
"https://github.com/leshchenko1979/fast-mcp-telegram/security/advisories/GHSA-xr72-j7vj-vp7g",
"https://nvd.nist.gov/vuln/detail/CVE-2026-55096",
"https://github.com/leshchenko1979/fast-mcp-telegram/commit/e6b3032cfc906e14f5b84f2c2b8ec378eb457e57"
],
"provider_metadata": {
"cwe_ids": [
"CWE-184",
"CWE-918"
],
"cna_assigner": "GitHub_M",
"unresolved_ranges": [
{
"extracted_events": [
{
"range": [
{
"fixed": "30.1"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
}
]
},
{
"extracted_events": [
{
"range": [
{
"fixed": "30.1"
},
{
"fixed": "30.1"
}
],
"source": "DESCRIPTION"
}
]
}
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55096.json"
}
},
"related_cves": [
{
"value": "CVE-2026-55096",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 494796,
"published_at": "2026-09-28T16:38:26.73+00:00"
}