Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to check integration URL for path traversal which allows an malicious authenticated user to call an arbitrary API via system admin Mattermost auth token using via path traversal in integration action URL.. Mattermost Advisory ID: MMSA-2026-00640
Casky was already ahead
This CVE exploits attack patterns that Casky's 331matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.
CVE-2026-4858 is a path traversal vulnerability in Mattermost versions 11.6.0 and earlier that fails to properly validate integration action URLs. An authenticated user can exploit this flaw to bypass normal API access controls by crafting malicious URLs with path traversal sequences (../) that allow them to call arbitrary Mattermost APIs using the system admin's authentication token. This is particularly dangerous because it affects multiple supported versions and requires only user-level authentication to trigger, making it accessible to insider threats or compromised low-privilege accounts. Organizations running affected Mattermost deployments face immediate risk of unauthorized API access, potential data exfiltration, and lateral movement within their communication infrastructure.
Casky.ai's 331 matching skills detect this attack pattern by mapping to MITRE ATT&CK techniques TA0001 (Initial Access) and TA0007 (Discovery). Using Claude's extended reasoning capabilities, the platform identifies the telltale indicators: suspicious integration URLs containing path traversal patterns (../ sequences), API calls originating from integration action handlers that don't match expected endpoints, and authentication token usage inconsistent with normal admin activity. Practitioners using Casky would see findings highlighting CWE-22 violations where user-supplied URL inputs flow directly into API requests without sanitization, coupled with detection of privilege escalation patterns where low-privilege authenticated sessions suddenly access admin-level APIs. The skill set would flag integration configurations as high-risk, correlate suspicious API calls with integration tokens, and surface the specific URL validation gaps that enable the exploit—enabling teams to prioritize patching and implement compensating controls like API request filtering.
Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →
These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-4858.
Casky has 331 skills that investigate the attack patterns behind CVE-2026-4858. Run one and get CVSS-scored findings in 3 minutes.
Run the skill that detects this →analyzing-office365-audit-logs-for-compromise
cloud security · low
analyzing-persistence-mechanisms-in-linux
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auditing-aws-s3-bucket-permissions
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cloud security · low
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detecting-misconfigured-azure-storage
cloud security · low
detecting-mobile-malware-behavior
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ot ics security · medium
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detecting-oauth-token-theft
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detecting-pass-the-hash-attacks
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threat hunting · low
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threat hunting · low
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detecting-serverless-function-injection
cloud security · low
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threat hunting · low
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api security · medium
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ot ics security · medium
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detecting-suspicious-powershell-execution
threat hunting · low
detecting-t1003-credential-dumping-with-edr
threat hunting · low
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threat hunting · low
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threat hunting · low
detecting-wmi-persistence
threat hunting · low
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penetration testing · medium
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red teaming · high
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api security · medium
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api security · medium
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web application security · medium
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red teaming · high
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mobile security · low
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api security · medium
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mobile security · low
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web application security · medium
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api security · medium
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threat hunting · low
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threat hunting · low
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threat hunting · low
hunting-for-persistence-mechanisms-in-windows
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threat hunting · low
hunting-for-spearphishing-indicators
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threat hunting · low
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threat hunting · low
hunting-for-suspicious-scheduled-tasks
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threat hunting · low
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threat hunting · low
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threat hunting · low
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phishing defense · medium
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devsecops · low
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vulnerability management · medium
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implementing-cloud-waf-rules
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devsecops · low
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ot ics security · medium
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ot ics security · medium
implementing-email-sandboxing-with-proofpoint
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devsecops · low
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cloud security · low
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devsecops · low
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phishing defense · medium
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ot ics security · medium
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ot ics security · medium
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devsecops · low
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phishing defense · medium
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mobile security · low
implementing-nerc-cip-compliance-controls
ot ics security · medium
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ot ics security · medium
implementing-ot-incident-response-playbook
ot ics security · medium
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ot ics security · medium
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devsecops · low
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devsecops · low
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devsecops · low
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mobile security · low
managing-cloud-identity-with-okta
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red teaming · high
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red teaming · high
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phishing defense · medium
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api security · medium
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api security · medium
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ot ics security · medium
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red teaming · high
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penetration testing · medium
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ot ics security · medium
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reverse-engineering-ios-app-with-frida
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scanning-containers-with-trivy-in-cicd
devsecops · low
scanning-infrastructure-with-nessus
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cloud security · low
securing-aws-lambda-execution-roles
cloud security · low
securing-azure-with-microsoft-defender
cloud security · low
securing-container-registry-images
cloud security · low
securing-github-actions-workflows
devsecops · low
securing-historian-server-in-ot-environment
ot ics security · medium
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cloud security · low
securing-remote-access-to-ot-environment
ot ics security · medium
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cloud security · low
testing-android-intents-for-vulnerabilities
mobile security · low
testing-api-authentication-weaknesses
api security · medium
testing-api-for-broken-object-level-authorization
api security · medium
testing-api-for-mass-assignment-vulnerability
api security · medium
testing-api-security-with-owasp-top-10
web application security · medium
testing-cors-misconfiguration
web application security · medium
testing-for-broken-access-control
web application security · medium
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web application security · medium
testing-for-email-header-injection
web application security · medium
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web application security · medium
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web application security · medium
testing-for-open-redirect-vulnerabilities
web application security · medium
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web application security · medium
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web application security · medium
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penetration testing · medium
testing-for-xss-vulnerabilities-with-burpsuite
web application security · medium
testing-for-xxe-injection-vulnerabilities
web application security · medium
testing-jwt-token-security
web application security · medium
testing-mobile-api-authentication
mobile security · low
testing-oauth2-implementation-flaws
api security · medium
testing-websocket-api-security
api security · medium
triaging-vulnerabilities-with-ssvc-framework
vulnerability management · medium
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