VulnerabilityPublished 28 Sep 2026Updated 1 Oct 2026

CVE-2026-55096: leshchenko1979 fast-mcp-telegram · Incomplete List of Disallowed Inputs

Affects leshchenko1979 fast-mcp-telegramSource CVE Database V5

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Not known to be exploited · CVSS 7.1 High : upgrade to 30.1 soon.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 3.1 base score

7.1High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 17% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 30.1

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

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

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade fast-mcp-telegram and leshchenko1979/fast-mcp-telegram to 30.1.

Affected software

Product	Affected	Fixed in
leshchenko1979fast-mcp-telegram	Affected <30.1	Fixed in 30.1
GitHubleshchenko1979/fast-mcp-telegram`pkg:github/leshchenko1979/fast-mcp-telegram`Other threats	Affected <30.1	Fixed in 30.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

This vulnerability is fixed in fast-mcp-telegram version 30.1. Users should upgrade to version 30.1 or later to remediate this issue. No additional mitigations are required once the patch is applied.

Description

fast-mcp-telegram versions prior to 30.1 contain a server-side request forgery (SSRF) vulnerability in the send_message and send_message_to_phone MCP tools. These tools accept files as lists of HTTP(S) URLs, which the server downloads and attaches to outgoing Telegram messages. The URL validation relies on a denylist that checks only the hostname string without DNS resolution, allowing attackers to bypass restrictions and cause the server to fetch resources from internal or private network addresses. This results in a full-read SSRF that can exfiltrate data by returning the fetched content as a Telegram file attachment. The vulnerability is patched in version 30.1.

Impact

An attacker with at least low privileges can exploit this SSRF vulnerability to cause the server to fetch internal or private network resources and exfiltrate their contents by embedding them as Telegram file attachments. This can lead to unauthorized disclosure of sensitive internal data. The CVSS score of 7.1 (high) reflects the network attack vector, low complexity, and high confidentiality impact, with no impact on availability and limited integrity impact.

Summary

The fast-mcp-telegram MCP server prior to version 30.1 has an SSRF vulnerability (CVE-2026-55096) due to incomplete validation of URLs provided to the send_message and send_message_to_phone tools. The server uses a denylist (_validate_url_security) that checks only the literal hostname string of URLs without performing DNS resolution. Because the actual HTTP client (httpx.AsyncClient.get) resolves DNS at request time, an attacker can supply hostnames that resolve to loopback, private, or link-local IP addresses, bypassing the denylist. The server fetches these URLs and attaches the fetched content to outgoing Telegram messages, enabling an attacker to read internal resources fully. This vulnerability is fixed in version 30.1.

CWE-184Incomplete List of Disallowed Inputs (opens in a new tab)
Base weaknessOWASP Top 10 A03:2021: Injection (opens in a new tab)
The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.
Implementation · Input Validation
Do not rely exclusively on detecting disallowed inputs. There are too many variants to encode a character, especially when different environments are used, so there is a high likelihood of missing some variants. Only use detection of disallowed inputs as a mechanism for detecting suspicious activity.
Attack patterns
Double Encoding (opens in a new tab)
Command Delimiters (opens in a new tab)
Flash Injection (opens in a new tab)
Using Leading 'Ghost' Character Sequences to Bypass Input Filters (opens in a new tab)
Exploiting Multiple Input Interpretation Layers (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-918Server-Side Request Forgery (opens in a new tab)
Base weaknessCWE Top 25 (2025): #22OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
Implementation · Operation
If there is a known list of applications, IP, hostname, and/or domains to which the product is allowed to communicate, then use allowlists to ensure that outgoing requests are restricted to these known entities. The allowlists could be in the application code or possibly enforced by firewalls or network segmentation.
Implementation · Operation
If the product is expected to be able to connect to arbitrary IP addresses or domains, consider using a denylist that includes private network addresses, internal domain names, etc. The denylist could be in the application code or possibly enforced by firewalls or network segmentation.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
OWASP Cheat Sheets
Server Side Request Forgery Prevention (opens in a new tab)
Unvalidated Redirects and Forwards (opens in a new tab)
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.6.1 (opens in a new tab)
V5.2.6 (opens in a new tab)
Attack patterns
Server Side Request Forgery (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 5 Oct 2026, 20:10 UTC

WeaknessesCWE-184, CWE-918

Technical details

References

Community reviews

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