Thumbnail disclosure via write-mode permission bypass
Published Jan 26, 2022 · Updated Apr 23, 2025
Improper permission control in Nextcloud Android App before 3.17.1 allows attackers to read cached image thumbnails through a local app. The exported DiskLruImageCacheFileProvider lacks a write permission and returns the same file descriptor regardless of open mode, so write-mode access bypasses MANAGE_DOCUMENTS. A malicious application must already run on the same Android device; exposure is limited to cached thumbnails, which can contain sensitive image data.
Summary
What happened
Improper permission control in Nextcloud Android App before 3.17.1 allows attackers to read cached image thumbnails through a local app. The exported DiskLruImageCacheFileProvider lacks a write permission and returns the same file descriptor regardless of open mode, so write-mode access bypasses MANAGE_DOCUMENTS. A malicious application must already run on the same Android device; exposure is limited to cached thumbnails, which can contain sensitive image data.
The record
- CVE
- CVE-2021-41166
- Published
- Jan 26, 2022
- Updated
- Apr 23, 2025
- Vendor
- Nextcloud GmbH
- Product
- Security Advisories
- Classifications
- CWE-276, T1409
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jan 26, 2022CVE publishedPublication date reported by the CVE source.
- Apr 23, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 3.17.1
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- DiskLruImageCacheFileProvider thumbnail-exfiltration PoCproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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