Security readout for executives and security teams
Plain-English summary
BookStack versions before 26.05.4 allow an editor to store a malicious SVG drawing. If an administrator later accesses it through the image gallery API, embedded script can run in the administrator’s browser, potentially exposing sensitive data or enabling unauthorized administrative actions.
Executive priority
Treat affected installations as an urgent remediation priority, especially where editors are numerous, externally managed, or less trusted. Schedule immediate inventory and upgrade work. The impact could cross the editor-to-administrator trust boundary, although public exploitation has not been established.
Technical view
The drawing upload endpoint accepts unvalidated base64 content and stores it without inspecting the decoded file. An editor can therefore store script-bearing SVG content. When retrieved through the image gallery API, missing content-type validation and CSP headers permit script execution in an administrator’s browser. This is stored cross-site scripting, classified as CWE-79.
Likely exposure
Exposure is limited to BookStack deployments earlier than 26.05.4 where an attacker has editor permissions and an administrator accesses the stored drawing. Internet reachability may increase opportunity, but the supplied evidence does not establish which deployments are exposed or whether default configurations are sufficient.
Exploitation context
The CVSS 4.0 score is 9.3. Exploitation requires low privileges and administrator interaction, but no attack complexity is identified. The supplied record says this CVE is not in KEV, and no cited evidence establishes active exploitation in the wild.
Researcher notes
The reported failure spans upload validation, stored-content inspection, response content-type handling, and CSP absence. Review the v26.05.4 patch when assessing remediation completeness. The supplied version range is summarized as “before 26.05.4”; no affected CPEs or configuration-specific exceptions are provided.
Mitigation direction
- Upgrade affected BookStack installations to version 26.05.4 or later.
- Review the vendor release notes and patch commit before deployment.
- Until upgraded, restrict editor permissions to trusted users.
- Consider disabling drawing uploads where operationally feasible pending vendor guidance.
Validation and detection
- Inventory BookStack deployments and confirm their installed versions.
- Identify installations earlier than version 26.05.4.
- Review editor accounts and remove unnecessary or untrusted access.
- Inspect stored drawings and upload records for unexpected SVG content.
- Confirm upgraded systems report version 26.05.4 or later.
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-79: 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-2026-84695 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
- Critical
- CVSS
- 9.3 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA: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
2 official scoresWe 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:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N——VulnCheckCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N2.35.8VulnCheckVulnerability scoring details
Base CVSS 4.0 score
9.3CriticalVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N
Base CVSS 3.1 score
8.7HighVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/BookStackApp/BookStackCVE reference, VulnCheck · product
- Patch CommitCVE reference, VulnCheck · patch
- https://github.com/BookStackApp/BookStack/blob/v26.05.3/app/Uploads/ImageService.phpCVE reference, VulnCheck · technical-description
- BookStack v26.05.4 Release NotesCVE reference, VulnCheck · release-notes
- https://www.bookstackapp.com/blog/bookstack-release-v26-05-4/CVE reference, VulnCheck · vendor-advisory
- VulnCheck Advisory: BookStack before 26.05.4 Stored XSS via Drawing UploadCVE reference, VulnCheck · third-party-advisory
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 Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.