CVE-2026-20915

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{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "[2.5.0b1,2.5.0b2)"}}], "enrichment": {"confidence": 95.0, "confidence_source": "inferred", "scores": [{"score": 95.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Checkmk", "source": "cna", "vendor": "Checkmk GmbH"}, "product": "checkmk", "vendor": "checkmk"}], "analysis": {"en": {"generated_at": "2026-04-02T13:24:26.417991+00:00", "value": {"mitigation_remediation": ["Apply the latest Checkmk release 2.5.0b2 or later to remove the stored XSS flaw", "Restrict permission to create pending changes to a narrow set of trusted users", "Validate or sanitize any user input that is stored for display in the sidebar", "Test the configuration changes in a staging environment before rolling out to production"], "summary": {"action": "Patch Immediately", "impact": "Remote JavaScript execution via stored XSS"}, "threat_synthesis": {"affected_systems": "Affecting deployments of Checkmk released by Checkmk GmbH, the flaw is present in Checkmk version 2.5.0 beta prior to the 2.5.0b2 update. The CPE strings cpe:2.3:a:checkmk:checkmk:* and cpe:2.3:a:checkmk:checkmk:2.5.0:b1:* identify the vulnerable product and version series.", "description_and_impact": "The vulnerability is a stored cross\u2011site scripting bug that occurs in the Pending Changes sidebar of Checkmk\u2019s 2.5.0 beta versions before the 2.5.0b2 release. Authenticated users who have permission to create pending changes can embed arbitrary JavaScript into the sidebar. When another user opens the sidebar, the injected script runs in that user\u2019s browser, allowing the attacker to steal session cookies, perform phishing, or tamper with user data. This is a classic stored XSS (CWE\u201179) that impacts confidentiality and integrity of data displayed in the UI.", "risk_and_exploitability": "The CVSS score of 8.5 indicates a high severity, while the EPSS score is below 1%, suggesting that widespread exploitation is currently unlikely and the flaw is not catalogued in CISA\u2019s KEV list. Nonetheless, the attack requires authenticated access with permission to create pending changes; an insider or compromised account can inject malicious code that will execute in the browsers of users who view the sidebar. Organizations that grant broad pending\u2011change permissions should be particularly vigilant, as the vulnerability can be leveraged to deliver client\u2011side attacks with the privileges of any user who consumes the sidebar content."}}}}, "created": "2026-03-31T19:54:37.873993+00:00", "updated": "2026-04-02T20:22:36.972474+00:00", "vendors": ["checkmk", "checkmk$PRODUCT$checkmk"]}