Security readout for executives and security teams
Plain-English summary
This Joomla core issue could let malformed input damage the CMS usergroups table, causing denial of service or administrative disruption. The source bundle identifies Joomla CMS versions 2.5.0 through 3.9.27 as affected. Severity and CVSS are not provided, so urgency depends on whether affected Joomla systems are still in production.
Executive priority
Treat this as a targeted cleanup item for legacy Joomla risk. It is not supported here as actively exploited, but affected production sites could suffer avoidable downtime or access-management disruption. Prioritize internet-facing and business-critical Joomla systems first.
Technical view
CVE-2021-26036 is a missing input validation issue in Joomla CMS core. The described outcome is a broken usergroups table, framed by Joomla as denial of service through usergroup table manipulation. The public bundle does not state authentication requirements, affected endpoints, CVSS scoring, CWE mapping, or exploit mechanics.
Likely exposure
Exposure is limited to Joomla CMS installations running versions 2.5.0 through 3.9.27. Public-facing sites, business-critical portals, and systems with complex user group permissions deserve priority review. The source bundle does not define whether exploitation requires credentials.
Exploitation context
The CVE is not listed as KEV in the provided bundle, and no cited source states active exploitation. The known impact is denial of service or operational disruption through usergroups table breakage. Practical exploitability is unclear from the available evidence.
Researcher notes
Available evidence is sparse. The bundle confirms affected versions and DoS impact, but lacks CVSS, CWE, prerequisites, endpoint details, and exploit status. Avoid assuming unauthenticated reachability. Validation should focus on version confirmation, exposure review, and table integrity rather than exploit reproduction.
Mitigation direction
- Identify Joomla CMS instances and confirm exact deployed versions.
- Upgrade affected Joomla systems to an unaffected version per Joomla guidance.
- Back up the database before remediation or recovery work.
- Review vendor advisory for any version-specific recovery instructions.
- Prioritize systems exposed to the internet or supporting critical business workflows.
Validation and detection
- Inventory Joomla sites and flag versions 2.5.0 through 3.9.27.
- Confirm usergroups table integrity and administrator access after updates.
- Review application logs for unusual usergroup or permission-related errors.
- Verify backups exist before applying CMS or database changes.
- Document systems where version or exposure cannot be confirmed.
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.
CVE-2021-26036 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
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
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 and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://developer.joomla.org/security-centre/857-20210702-core-dos-through-usergroup-table-manipulation.htmlCVE reference · x_refsource_MISC, vendor-advisory
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.