Security readout for executives and security teams
Plain-English summary
A Nextcloud File Drop link meant to allow uploads only could be bypassed when the Richdocuments app was installed. That could let an unauthenticated attacker read files from that share, turning a restricted public upload workflow into a confidentiality breach.
Executive priority
Treat as high priority where public File Drop links were used for confidential intake. The issue is confidentiality-focused, remotely reachable, and unauthenticated by CVSS, but current provided evidence does not establish active exploitation.
Technical view
CVE-2021-37628 is a CWE-639 authorization bypass in Nextcloud Richdocuments. Affected versions are below 3.8.4 and 4.0.0 through below 4.2.1. The CVSS 3.1 vector indicates network access, low complexity, no privileges, no user interaction, and high confidentiality impact only.
Likely exposure
Exposure is most likely on Nextcloud deployments using affected Richdocuments versions and File Drop, also described as Upload Only public link shares. The bundle does not identify affected Nextcloud Server versions beyond the Richdocuments app ranges.
Exploitation context
The public sources state an attacker was able to read arbitrary files in such a share. The bundle does not show CISA KEV listing or cited evidence of active exploitation in the wild.
Researcher notes
The strongest source facts are the GitHub advisory, CVE record, and HackerOne report reference. The root issue is an authorization bypass in Richdocuments interaction with upload-only public shares. Do not assume broader Nextcloud product impact without vendor confirmation.
Mitigation direction
- Upgrade Nextcloud Richdocuments to 3.8.4 or 4.2.1 as applicable.
- Disable the Richdocuments application if upgrading cannot be completed promptly.
- Review Nextcloud’s security advisory before choosing a remediation path.
- Prioritize exposed File Drop workflows that handle sensitive uploads.
Validation and detection
- Inventory Nextcloud instances for installed Richdocuments app versions.
- Confirm no deployment runs Richdocuments below 3.8.4 or 4.0.0 through below 4.2.1.
- Identify public Upload Only/File Drop shares on affected instances.
- After remediation, confirm upload-only shares do not allow file reads.
- Review share access records for unexpected reads where logging is available.
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-639: 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-2021-37628 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
- High
- CVSS
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:N/UI:N/S:U/C:H/I:N/A:N3.93.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-pxhh-954f-8w7wCVE reference · x_refsource_CONFIRM
- https://github.com/nextcloud/richdocuments/pull/1664CVE reference · x_refsource_MISC
- https://hackerone.com/reports/1253403CVE 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.
Authorization Bypass Through User-Controlled Key
Authorization Bypass Through User-Controlled Key represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.