Security readout for executives and security teams
Plain-English summary
This flaw lets any authenticated Nextcloud user lock files belonging to other users when the End-to-End Encryption app is vulnerable. The business impact is availability: affected users may be blocked from accessing or working with files. The sources do not provide CVSS scoring or evidence of active exploitation.
Executive priority
Schedule remediation promptly for any affected Nextcloud environment, especially shared or externally accessible deployments. This is not KEV-backed emergency evidence, but authenticated denial of access to business files can disrupt operations.
Technical view
CVE-2021-22906 affects Nextcloud End-to-End Encryption before 1.5.3, 1.6.3, and 1.7.1. It is described as a denial-of-service issue caused by improper permission handling around file locking. The assigned weakness is CWE-400, resource consumption. Exploitation requires an authenticated user according to the CVE description.
Likely exposure
Exposure is limited to Nextcloud deployments using the End-to-End Encryption app below the fixed 1.5.3, 1.6.3, or 1.7.1 releases. Risk is higher where many low-trust or external users have authenticated access.
Exploitation context
The provided sources describe a public vulnerability report and a Nextcloud advisory, but do not show active exploitation. The CVE is not marked as CISA KEV in the bundle. Treat exploitation status as unconfirmed beyond public disclosure.
Researcher notes
The source bundle lacks CVSS metrics, patch details beyond fixed versions, and evidence of exploitation in the wild. Analysis should remain scoped to authenticated denial of service through unauthorized file locking in the Nextcloud End-to-End Encryption app.
Mitigation direction
- Upgrade Nextcloud End-to-End Encryption to 1.5.3, 1.6.3, 1.7.1, or later.
- Review the Nextcloud advisory for branch-specific upgrade guidance.
- Prioritize systems with external, shared, or low-trust authenticated users.
- If immediate upgrade is blocked, check vendor guidance for temporary controls.
Validation and detection
- Inventory all Nextcloud instances using the End-to-End Encryption app.
- Confirm installed app versions are at or above the fixed releases.
- Review access models for untrusted authenticated users.
- Check support reports for unexplained file locking or availability issues.
- Document remediation status for each affected Nextcloud instance.
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-400: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. 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-2021-22906 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://hackerone.com/reports/1189174CVE reference · x_refsource_MISC
- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-3829-45wm-ww36CVE reference · x_refsource_MISC
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.
Uncontrolled Resource Consumption
Uncontrolled Resource Consumption represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.