Security readout for executives and security teams
Plain-English summary
Joomla Event Manager versions 1.0.0 through 5.0.0 allow a privileged administrator to upload dangerous files, including PHP. This could convert a compromised or malicious administrator account into control of the underlying web server, threatening site data, availability, and connected systems.
Executive priority
Treat as an urgent remediation for every affected internet-facing or business-critical Joomla site. Prioritize upgrades where administrator credentials may be shared, weakly protected, or recently exposed. Although active exploitation is not established, the potential consequence is server compromise and possible impact to connected systems.
Technical view
The administrator source model inadequately restricts uploaded file types, permitting PHP files and resulting in remote code execution. The issue is classified as CWE-434 and requires network access, high privileges, low complexity, and no user interaction. CVSS 4.0 rates impact across the vulnerable and subsequent systems as high.
Likely exposure
Exposure is limited to Joomla installations running JEM 1.0.0 through 5.0.0. Exploitation requires a highly privileged account, but stolen administrator credentials or a malicious administrator could provide that access. The supplied sources do not establish whether vulnerable functionality is enabled by default.
Exploitation context
The CVE is not listed as KEV in the supplied bundle, and no cited source reports active exploitation or public exploit availability. The prerequisite of high privileges reduces initial access likelihood, but successful exploitation could enable full server-side code execution with broad confidentiality, integrity, and availability impact.
Researcher notes
Evidence supports privileged unrestricted file upload leading to PHP execution, but provides no endpoint details, configuration prerequisites, exploit observations, or forensic indicators. Validate exposure defensively without attempting code execution. Version boundaries are explicit: 1.0.0 through 5.0.0 are affected; the title identifies versions below 5.0.1 as vulnerable.
Mitigation direction
- Upgrade Joomla Event Manager to version 5.0.1 or later after confirming vendor guidance and compatibility.
- Restrict administrator access to trusted personnel and require strong, phishing-resistant authentication.
- Temporarily limit access to affected administrative functionality if immediate upgrading is impossible.
- Review vendor guidance for additional remediation or configuration requirements.
Validation and detection
- Inventory Joomla sites and confirm the installed Joomla Event Manager version.
- Verify no deployed instance runs JEM versions 1.0.0 through 5.0.0.
- Review administrator accounts and authentication records for unauthorized or anomalous access.
- Inspect web-accessible directories for unexpected PHP files or recent unauthorized changes.
- Confirm the upgraded extension version and retest administrative upload restrictions.
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-434: File access and web shell behavior lookup
File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-77991 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
- Critical
- CVSS
- 9.4 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
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.
SSVC decision data
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:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H——JoomlaVulnerability scoring details
Base CVSS 4.0 score
9.4CriticalVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://www.joomlaeventmanager.net/CVE reference, Joomla · product
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.
Unrestricted Upload of File with Dangerous Type
Unrestricted Upload of File with Dangerous Type represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.