Security readout for executives and security teams
Plain-English summary
CVE-2021-39186 is a stored cross-site scripting issue in Miraheze's GlobalNewFiles MediaWiki extension. A crafted account name could be displayed unsafely on the GlobalNewFiles special page, causing script execution when another user views it. Impact is limited in the CVSS record, but public wiki environments should treat it as a prompt hygiene and user-trust risk.
Executive priority
Treat as a moderate-priority web application fix. It is not described as actively exploited and has limited CVSS impact, but stored XSS can damage user trust and create session-level workflow risk for staff who view affected pages.
Technical view
Before commit cee254e1b158cdb0ddbea716b1d3edc31fa4fb5d, GlobalNewFiles did not properly validate or encode usernames in the username column of its special page. The CVE classifies this as CWE-20 with CVSS 3.1 score 4.3, network reachable, low complexity, no privileges required, user interaction required, and low integrity impact.
Likely exposure
Exposure is limited to MediaWiki deployments using the Miraheze GlobalNewFiles extension before the named patch commit. Risk is higher where account creation is open and users or staff view the GlobalNewFiles special page. The sources do not provide conventional version numbers or package names.
Exploitation context
The source bundle does not show CISA KEV listing or cite active exploitation. Practical abuse requires a victim to view the affected special page after a maliciously formed username is present. Sources describe the weakness and patch, but do not provide exploitation evidence.
Researcher notes
The key constraint is affected-version ambiguity: sources identify the vulnerable range by commit rather than release numbers. Validation should focus on source state, deployed extension revision, account-name controls, and safe output handling on the GlobalNewFiles special page. Avoid assuming impact beyond low integrity impact stated in CVSS.
Mitigation direction
- Update GlobalNewFiles to include commit cee254e1b158cdb0ddbea716b1d3edc31fa4fb5d or later.
- Check vendor advisory and repository guidance for supported upgrade handling.
- As a temporary workaround, restrict account names from using HTML or script-enabling characters.
- Review username policy for public-registration wikis using this extension.
- Prioritize remediation where administrators routinely view GlobalNewFiles.
Validation and detection
- Inventory MediaWiki instances for the GlobalNewFiles extension.
- Compare deployed extension code against patch commit cee254e1b158cdb0ddbea716b1d3edc31fa4fb5d.
- Confirm account-name validation blocks unsafe HTML-related characters if relying on the workaround.
- Verify the GlobalNewFiles special page renders usernames as inert text after patching.
- Document whether affected public routes and operational behavior changed.
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-20: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-39186 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 4.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/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:N/UI:R/S:U/C:N/I:L/A:N2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/miraheze/GlobalNewFiles/security/advisories/GHSA-57p5-hqjq-h7vgCVE reference · x_refsource_CONFIRM
- https://github.com/miraheze/GlobalNewFiles/commit/cee254e1b158cdb0ddbea716b1d3edc31fa4fb5dCVE reference · x_refsource_MISC
- https://phabricator.miraheze.org/T7935CVE 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.