Security readout for executives and security teams
Plain-English summary
Older Nextcloud Android clients could expose image thumbnails to another app that should not have access. The disclosed impact is limited to confidentiality of thumbnails, not full file control, integrity, or availability. Version 3.17.1 fixes the issue, and the source bundle states there are no known workarounds.
Executive priority
Handle as a routine but necessary mobile client update. Raise priority where Nextcloud stores regulated, confidential, or customer image content. The business risk is privacy exposure from thumbnails, not broad system compromise based on the supplied evidence.
Technical view
CVE-2021-41166 affects Nextcloud Android App versions before 3.17.1. An unauthorized app without the normally required MANAGE_DOCUMENTS permission may view image thumbnails it is not permitted to view. The issue is mapped to CWE-276 and scored CVSS 3.1 4.3 with low confidentiality impact only.
Likely exposure
Exposure is limited to Android devices running the Nextcloud app below 3.17.1, especially where sensitive images are handled through Nextcloud. Server-side Nextcloud products are not identified as affected in the provided sources.
Exploitation context
The source bundle does not report known active exploitation, and KEV status is false. The described scenario requires an unauthorized Android app able to access thumbnails through the permission bypass. Evidence is sufficient for exposure triage, but not for claims about exploitation in the wild.
Researcher notes
Focus on Android client version exposure and thumbnail access controls. The advisory names a permission bypass involving MANAGE_DOCUMENTS and patched version 3.17.1. The provided sources do not support active exploitation claims, alternative mitigations, or broader affected-product assertions.
Mitigation direction
- Update Nextcloud Android App to version 3.17.1 or later.
- Enforce a minimum app version through MDM or managed app distribution.
- Remove or block unsupported older Android client builds.
- Check vendor guidance if immediate updating is not possible.
- Do not rely on configuration workarounds; sources state none are known.
Validation and detection
- Inventory Android devices with the Nextcloud app installed.
- Identify any installations below version 3.17.1.
- Confirm managed app stores distribute only patched versions.
- Review whether sensitive images are accessed from affected Android clients.
- Track remediation completion for BYOD and managed devices separately.
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-276: 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-2021-41166 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
- 4.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
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:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://hackerone.com/reports/1358597CVE reference · x_refsource_MISC
- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-wrwg-jwpg-r3c4CVE reference · x_refsource_CONFIRM
- https://github.com/nextcloud/android/commit/aa47197109970b8449c4e44601eba36e3481b086CVE reference · x_refsource_MISC
- https://github.com/nextcloud/android/commit/b6ecf515b38c2d82d32743f27236534f3e03ee0cCVE 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.
Incorrect Default Permissions
Incorrect Default Permissions represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.