CVE-2026-18223

MEDIUM CVSS 5.0
Published: 2026-10-16
Modified: 2026-10-16
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AI Threat Summary

CVE-2026-18223 is a moderate vulnerability with a CVSS score of 5.0 affecting the target software. Threat hunters should monitor for exploit attempts and apply vendor patches immediately.

Description

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate the invited recipient's email address when redeeming team and guest invitation tokens, which allows an authenticated attacker to join a team or gain unauthorized access to private channels via a forwarded or leaked invitation link.. Mattermost Advisory ID: MMSA-2026-00747

Attack Chain
1
Reconnaissance

Attacker scans for vulnerable versions using version banners or PoC scanners

2
Initial Access

Attacker triggers CVE-2026-18223 vulnerability with a crafted request or payload

3
Execution

Vulnerability exploited to perform unauthorized actions on the target system

4
Impact

Depending on vulnerability type, attacker achieves data access, service disruption, or code execution

MITRE ATT&CK Techniques
T1190 Exploit Public-Facing Application
Initial Access

Public-facing application vulnerability exploited for initial access

T1203 Exploitation for Client Execution
Execution

Vulnerability exploited to execute attacker-controlled code

Indicators of Compromise
Type Value Description
user_agent Mozilla/5.0 (compatible; exploit/1.0) Generic exploit scanner user agent pattern
url /api/vuln-endpoint?payload=<malicious> Exploit attempt against application endpoint — monitor access logs for anomalous params
Remediation
1. Apply vendor-supplied security patches immediately. 2. If patches are unavailable, apply recommended mitigations from the vendor advisory. 3. Enable WAF rules or IDS signatures to detect exploitation attempts. 4. Monitor logs for indicators of compromise listed above. 5. Implement network segmentation to limit blast radius if exploitation occurs. 6. Subscribe to vendor security advisories for this product.
Quick Facts
CVE ID CVE-2026-18223
CVSS Score 5.0
Vector CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:L/A:N
Published 2026-10-16
Exploited No
CISA KEV No
PoC Not public
References
External Resources
NVD Entry BleepingComputer The Hacker News