CVE-2026-55096 SSRF via DNS-resolution gap in _validate_url_security (file download by URL)
An attacker can exploit a DNS resolution gap to perform Server-Side Request Forgery and exfiltrate internal data via file downloads.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-55096?
CVE-2026-55096 is a high-severity server-side request forgery vulnerability in leshchenko1979 fast-mcp-telegram, published on 28 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-55096?
How do I fix CVE-2026-55096?
No fix has been published for CVE-2026-55096 yet. Limit exposure of the affected software until one is available.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-55096 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55096 exists.
Sources
Also known as GHSA-xr72-j7vj-vp7g.