Trending
CVE-2026-4339

CVE detail

CVE-2026-4339

Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery (SSRF) and exfiltrate data from internal network services via supplying internal URLs as file attachments in post creation requests.. Mattermost Advisory ID: MMSA-2026-00635

CVSS 6.5 · MediumBuzz score 11.9

Buzz score

Why this CVE is surfacing

Buzz score total 11.9

This all-time snapshot uses the same composite formula as Trending across a 30-year evidence window, rather than a current rolling window.

Buzz score components · mention 6.9 · diversity 5.0 · KEV 0.0 · OTX 0.0 · PoC 0.0

Mention score

6.9

1 evidence mentions in the snapshot

Diversity score

5.0

1 sources across 1 categories

KEV score

0.0

No KEV entry observed

OTX score

0.0

0 OTX pulses

PoC score

0.0

0 repos · best confidence N/A

Best PoC traction

Maximum stars on a matched PoC repo

Why it matters now

Mention timeline

Total mentions: 0; within the 30d window
Peak daily: 0; highest bucket

Evidence

Source links by recency

Newest mentions first

1 source links · newest first

https://mattermost.com/security-updatesmattermost.com
No excerpt available.
Vendor Advisorymattermost.comJun 26, 2026, 3:16 PM

Exploit code

Public exploit repository references

Public PoC repositories are third-party, potentially unsafe artifacts. Treat their code as untrusted and use it only on authorized systems in an isolated, least-privilege environment. cvebuzz does not execute the code or verify that an exploit works.

0 repository references · best confidence N/A · max 0 stars

No public PoC repositories have been matched yet.

Related records

Similar CVEs

6 related CVEs with shared weakness or product evidence

CVE-2026-6333
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1 mention
CVE-2026-2455
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation which allows an attacker…
CVSS 4.3 · Medium
1 mention
CVE-2025-47700
Mattermost Server versions 10.5.x <= 10.5.9 utilizing the Agents plugin fail to reject empty request bodies which allows users to trick users into clicking malicious links via pos…
CVSS 3.5 · Low
CVE-2024-45843
Mattermost versions 9.5.x <= 9.5.8 fail to include the metadata endpoints of Oracle Cloud and Alibaba in the SSRF denylist, which allows an attacker to possibly cause an SSRF if M…
CVSS 3.1 · Low
CVE-2023-3577
Mattermost fails to properly restrict requests to localhost/intranet during the interactive dialog, which could allow an attacker to perform a limited blind SSRF.
CVSS 3.5 · Low
CVE-2019-20872
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CVSS 5.5 · Medium

External lookup

Potential internet exposure

Potential exposure only — not proof of vulnerability.Shodan results indicate potentially internet-exposed products, not confirmed vulnerable systems. They do not confirm that any returned system is vulnerable to CVE-2026-4339.

Product-level CPE searches intentionally omit version fields and NVD version-range or configuration certainty. Verify the exact product version and configuration independently.

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Product CPE queries

Derived from this CVE's existing NVD CPE 2.3 records; the application, operating-system, or hardware part is retained.

cpe:2.3:a:mattermost:mattermost_serverSearch this product on Shodan

Exact CVE query

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Metadata

Canonical fields

NVD status

Analyzed

Published

Jun 26, 2026

Modified

Jun 29, 2026

Official record

Authoritative NVD record

CVSS vector

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

CWE IDs

Vendor classifications

How this vector reads

CVSS 3.1 base metrics decoded below. This explanation does not recalculate or change the NVD score.

Attack Vector (AV): Local. The attacker needs local access to the vulnerable system.
Attack Complexity (AC): Low. No special conditions beyond the attacker-controlled steps are required.
Privileges Required (PR): Low. The attacker needs basic user-level privileges.
User Interaction (UI): None. Exploitation does not require another user to act.
Scope (S): Changed. Impacts can cross into a different security authority.
Confidentiality Impact (C): High. There is a total or serious impact to this security property.
Integrity Impact (I): None. There is no direct impact to this security property.
Availability Impact (A): None. There is no direct impact to this security property.

Signals

Exploitation indicators

0 stored signals · no KEV · 0 OTX pulses