Security readout for executives and security teams
Plain-English summary
HedgeDoc versions before 1.8.2 can let someone who can edit a note place JavaScript into note metadata. On guest-editable instances, this may include unauthenticated users. Successful abuse could expose user data or alter page behavior when a victim views the note.
Executive priority
Treat this as a high-priority web application fix if HedgeDoc is internet-facing or guest-editable. The patch is identified, and disabling guest edits is a practical interim control. Prioritize before broader content or configuration cleanup.
Technical view
CVE-2021-29503 is a CWE-80 cross-site scripting issue in HedgeDoc note YAML metadata. Open Graph metadata could render unsafe HTML into the page head. Affected versions are HedgeDoc before 1.8.2. CVSS 3.1 is 8.1, with network access, low complexity, and user interaction required.
Likely exposure
Exposure is limited to HedgeDoc deployments running versions earlier than 1.8.2. Risk is higher where notes allow guest editing, because the advisory says unauthenticated attackers may inject JavaScript into guest-editable notes.
Exploitation context
The provided sources do not show active exploitation, and this CVE is not marked KEV in the bundle. Exploitation requires a victim to view an affected note and requires note write access, unless guest editing is enabled.
Researcher notes
Focus validation on version, guest-edit configuration, and note write-access boundaries. The source bundle identifies the vulnerable path as YAML metadata used for Open Graph rendering into the head section. Do not assume other HedgeDoc branches or forks are affected without vendor evidence.
Mitigation direction
- Upgrade HedgeDoc to version 1.8.2 or later.
- Disable guest edits until the update is complete.
- Review note permission settings for broad write access.
- Check HedgeDoc vendor advisory and release notes for deployment-specific guidance.
Validation and detection
- Inventory all HedgeDoc instances and record installed versions.
- Confirm no production instance runs HedgeDoc before 1.8.2.
- Verify guest editing is disabled where upgrade is pending.
- Review exposed shared notes for unexpected metadata changes.
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-80: 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-2021-29503 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
- 8.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/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:R/S:U/C:H/I:H/A:N2.85.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.1HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-gjg7-4j2h-94fqCVE reference · x_refsource_CONFIRM
- https://github.com/hedgedoc/hedgedoc/commit/01dad5821ee28377ebe640c6c72c3e0bb0d51ea7CVE reference · x_refsource_MISC
- https://github.com/hedgedoc/hedgedoc/releases/tag/1.8.2CVE 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.
Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.