Security readout for executives and security teams
Plain-English summary
CVE-2026-21483 affects self-hosted listmonk before 6.0.0. A lower-privileged user with campaign management rights can plant stored JavaScript in campaigns or templates. If a Super Admin views the content, the script can act as that admin, including creating backdoor admin accounts.
Executive priority
Treat as a timely upgrade for any multi-user listmonk deployment. Although rated medium, the practical impact can be admin account takeover if an internal lower-privileged user or compromised account can manage campaigns.
Technical view
This is stored cross-site scripting, CWE-79, in listmonk <6.0.0. The advisory describes malicious JavaScript injection through campaign or template content by users with campaign management permissions. Execution occurs in a Super Admin browser context and can cause high confidentiality and integrity impact. Public archives may allow triggering when a victim visits a link.
Likely exposure
Exposure is limited to organizations running self-hosted listmonk versions earlier than 6.0.0, especially where non-admin users can manage campaigns or templates. Public archive use may increase exposure because preview interaction is not required according to the advisory.
Exploitation context
The provided sources do not show CISA KEV listing or confirmed active exploitation. Exploitation requires an authenticated lower-privileged user with campaign management permissions, then execution in a higher-privileged user's browser or via public archive access.
Researcher notes
Evidence is based on the CVE record and GitHub advisory. The CVSS v4 score is 5.4, with low attack complexity and low privileges required. No exploit code or confirmed in-the-wild exploitation is cited in the provided sources.
Mitigation direction
- Upgrade listmonk to version 6.0.0 or later.
- Review vendor advisory for any additional configuration guidance.
- Restrict campaign and template management permissions to trusted users.
- Review public archive exposure until the upgrade is complete.
Validation and detection
- Inventory listmonk deployments and identify versions below 6.0.0.
- List users with campaign or template management permissions.
- Check whether public archives are enabled on affected instances.
- Review admin accounts for unexpected additions or privilege changes.
- Confirm upgraded systems report listmonk 6.0.0 or later.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-21483 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.4 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:P
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:P——Primary CVE scoreVulnerability scoring details
Base CVSS 4.0 score
5.4MediumVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:P
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/knadh/listmonk/security/advisories/GHSA-jmr4-p576-v565CVE reference · x_refsource_CONFIRM
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.