# 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.

- **Severity:** High 7.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 28 Sep 2026
- **Updated:** 1 Oct 2026
- **Also known as:** GHSA-xr72-j7vj-vp7g

## 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.

Weakness: CWE-918 (Server-Side Request Forgery), CWE-184 (Incomplete List of Disallowed Inputs)

## 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.

## Is CVE-2026-55096 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55096 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55096 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55096 exists.

Affected product: leshchenko1979 fast-mcp-telegram. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55096/ (Markdown: https://insights.sbomify.com/CVE-2026-55096/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55096
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55096
- OSV: https://osv.dev/vulnerability/CVE-2026-55096

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55096/
Summaries are generated and may contain mistakes; the official description above is the record.