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CVE-2026-4983 Eclipse Foundation CVE debrief

CVE-2026-4983 is a stored cross-site scripting (XSS) vulnerability in the Open VSX Registry. The vulnerability arises from the lack of sanitization of SVG files uploaded as extension icons before they are stored. These SVG files are served with a Content-Type of image/svg+xml and without security headers such as Content-Security-Policy or Content-Disposition: attachment. An attacker can exploit this by publishing an extension with a malicious SVG icon. When a user navigates directly to the icon URL, the malicious script is executed. The impact of this vulnerability varies depending on the deployment. For deployments using local storage, script execution occurs within the Open VSX application origin, which can lead to session hijacking, authentication token theft, and unauthorized extension publishing. For deployments backed by external storage, such as open-vsx.org with an S3-backed CDN, the execution is confined to the storage origin, reducing the impact but still allowing for phishing attacks and credential harvesting through attacker-crafted pages.

Vendor
Eclipse Foundation
Product
Eclipse Open VSX
CVSS
MEDIUM 4.1
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-23
Original CVE updated
2026-06-24
Advisory published
2026-06-23
Advisory updated
2026-06-24

Who should care

Organizations and individuals using Open VSX Registry, especially those hosting their own instances or using deployments with local storage, should be concerned about CVE-2026-4983. This vulnerability can lead to significant security risks, including session hijacking and unauthorized publishing of extensions, which can compromise the integrity and security of the development environment. Users of Open VSX Registry should assess their exposure and take necessary actions to mitigate this vulnerability.

Technical summary

The Open VSX Registry does not properly sanitize SVG files used as extension icons before storing and serving them. This allows an attacker to upload a malicious SVG file that can execute script when directly accessed. The vulnerability's impact depends on the deployment type. In local storage deployments, the script runs within the Open VSX application origin, enabling session hijacking, authentication token theft, and unauthorized extension publishing. In externally stored deployments, impact is reduced but still allows phishing and credential harvesting.

Defensive priority

CVE-2026-4983 has a CVSS score of 4.1 and is classified as MEDIUM severity. Given its potential for stored XSS attacks, especially in local storage deployments, it is crucial for affected organizations to prioritize patching or mitigating this vulnerability.

Recommended defensive actions

  • Immediately update Open VSX Registry to version 0.34.1 or later to ensure SVG sanitization.
  • Review and sanitize all existing extension icons to prevent exploitation.
  • Implement additional security headers such as Content-Security-Policy and Content-Disposition: attachment for serving SVG files.
  • Monitor for and restrict direct access to SVG files served by the Open VSX Registry.
  • Educate users about the risks of navigating to untrusted extension icons.

Evidence notes

The CVE-2026-4983 details were obtained from the NVD and CVE.org. The vulnerability was disclosed and made public on June 23, 2026. The Open VSX Registry's handling of SVG files allows for stored XSS attacks, with varying impacts based on deployment configurations.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-4983 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-4983

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-4983 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-4983

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.