Security readout for executives and security teams
Plain-English summary
This Nextcloud issue can make a downloaded file look harmless in the interface while saving with a more dangerous extension. It requires a logged-in attacker and a user who downloads the file. Business risk is limited but real for organizations relying on Nextcloud file-sharing trust.
Executive priority
Treat as a routine patching item unless affected Nextcloud instances handle high-risk user uploads. Prioritize upgrade during the next maintenance window, with added attention to custom or third-party Nextcloud apps.
Technical view
Controllers using Nextcloud Server DownloadResponse did not escape filenames by default. If an application passed an unsanitized user-supplied filename, UI behavior could show a benign extension while the actual download used another extension. Fixed in 19.0.13, 20.0.11, and 21.0.3. CWE-116 applies.
Likely exposure
Exposure is most likely on Nextcloud Server instances running below 19.0.13, 20.0.11, or 21.0.3, especially where apps use DownloadResponse with user-controlled filenames.
Exploitation context
The provided sources do not show known active exploitation, and the CVE is not marked KEV. Exploitation requires authentication and user interaction, with impact limited to file-download deception and low integrity impact.
Researcher notes
The impact depends on whether an app passes unsanitized user-controlled filenames into DownloadResponse. Available evidence supports a low-severity output-escaping flaw, not remote code execution or unauthenticated compromise. No source in the bundle establishes exploitation in the wild.
Mitigation direction
- Upgrade Nextcloud Server to 19.0.13, 20.0.11, 21.0.3, or later.
- Apply Fedora or Gentoo package updates where Nextcloud is distro-managed.
- Review custom Nextcloud apps using DownloadResponse with user-supplied filenames.
- Developers should escape filenames before passing them into DownloadResponse.
- Do not rely on an admin workaround; none is named in the advisory.
Validation and detection
- Inventory Nextcloud Server versions across all managed instances.
- Confirm no instance remains in the affected version ranges.
- Review custom app controllers for DownloadResponse filename handling.
- Verify user-controlled filenames are escaped before download responses.
- Check distro advisory status if using packaged Nextcloud builds.
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-116: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. 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-2021-32679 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
- Low
- CVSS
- 3.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/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:R/S:U/C:N/I:L/A:N2.11.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
3.5LowVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-3hjp-26x8-mhf6CVE reference · x_refsource_CONFIRM
- https://github.com/nextcloud/server/pull/27354CVE reference · x_refsource_MISC
- https://hackerone.com/reports/1215263CVE reference · x_refsource_MISC
- FEDORA-2021-9b421b78afCVE reference · vendor-advisory, x_refsource_FEDORA
- FEDORA-2021-6f327296feCVE reference · vendor-advisory, x_refsource_FEDORA
- GLSA-202208-17CVE reference · vendor-advisory, x_refsource_GENTOO
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.
Improper Encoding or Escaping of Output
Improper Encoding or Escaping of Output represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.