Security readout for executives and security teams
Plain-English summary
CVE-2021-3987 lets an authenticated calibre-web user create public shelves even when they lack public shelf permissions. This can cause unauthorized content organization or exposure decisions inside the application, but the cited severity is medium and no source indicates active exploitation.
Executive priority
Treat as a medium-priority access-control issue. Prioritize internet-facing or shared-user calibre-web deployments, especially where public shelves can disclose sensitive library metadata or content organization.
Technical view
The flaw is improper access control in janeczku/calibre-web. The create_shelf method in shelf.py did not verify whether the current user had permission to create a public shelf. CVSS 3.0 is 5.4 with low attack complexity, low privileges required, no user interaction, and limited confidentiality and integrity impact.
Likely exposure
Exposure is likely limited to deployments of janeczku/calibre-web with authenticated users who should not be able to create public shelves. The source bundle does not identify exact affected versions.
Exploitation context
Sources indicate this is remotely reachable by a logged-in low-privileged user. KEV is false, and the provided sources do not claim active exploitation in the wild.
Researcher notes
Evidence is narrow but consistent: the reported issue is a missing authorization check in create_shelf. Affected versions are unspecified in the provided bundle, so version-scoped conclusions should come from vendor or repository history.
Mitigation direction
- Review upstream calibre-web guidance for affected versions and remediation.
- Apply the upstream fix represented by the referenced GitHub commit where applicable.
- Limit account creation and authenticated access until patched.
- Audit shelf permissions for unintended public shelves.
Validation and detection
- Inventory all janeczku/calibre-web deployments and deployed versions.
- Confirm whether shelf.py includes a permission check before public shelf creation.
- Test in a controlled environment that low-privileged users cannot create public shelves.
- Review logs and shelf records for unauthorized public shelf creation.
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
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ATT&CK lookup starting points
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CWE-284: Authorization and privilege behavior lookup
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Open ATT&CK lookupCVE-2021-3987 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.4 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/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:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N2.82.5Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
5.4MediumVector: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Source materials
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 Access Control
Improper Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.