EUVD-2026-62546Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Space admin role required (PR:H); victim must view notification (UI:R); XSS executes in victim browser context, constituting a scope change (S:C) with limited session-level confidentiality and integrity impact.
Primary rating from Vendor (Fluid Attacks).
CVSS VectorVendor: Fluid Attacks
Lifecycle Timeline
3DescriptionCVE.org
HumHub 1.18.4 contains a stored cross-site scripting vulnerability in the comment-deletion notification flow. A Space administrator can delete another user's comment, choose to notify the original author, and place HTML/JavaScript in the deletion reason.
AnalysisAI
Stored cross-site scripting in HumHub 1.18.4 lets a Space administrator embed arbitrary HTML or JavaScript into the deletion-reason field of a comment-removal notification sent to the comment's original author. When the victim renders the notification in their browser, the injected script executes within their authenticated HumHub session, enabling session-token theft or unauthorized actions on their behalf. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the attacker to hold the Space administrator role within a HumHub Space - this is an elevated but internal platform role, not a server-level or global platform administrator. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 7.2 is driven by high-impact outcomes (VC:H/VI:H against the victim session) tempered by meaningful access barriers: PR:H confirms a Space administrator account is required, and AT:P/UI:P confirms the victim must actively render the notification. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | The upstream fix is available in GitHub Pull Request #8365 at https://github.com/humhub/humhub/pull/8365, which applies Html::encode() to the 'reason' field in CommentDeleted.php and to both the 'reason' and 'contentTitle' fields in ContentDeleted.php. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all HumHub instances running version 1.18.4 or earlier and determine exposure level; audit space administrator activity for any suspicious use of comment deletion features. …
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External POC / Exploit Code
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