CVE-2026-55876 Helium: Stored XSS via Unrestricted SVG File Upload — Authenticated Users Can Store Executable Scripts
Authenticated users can upload malicious SVG files to execute scripts in victim browsers, enabling phishing and content manipulation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-55876?
CVE-2026-55876 is a low-severity cross-site scripting vulnerability in HeliumEdu platform, published on 15 Oct 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Helium is a free online student planner for classes, homework, grades, and notes. Prior to 2.2.60, the POST /planner/attachments/ endpoint allows authenticated users to upload SVG and HTML attachments because conf/configs/common.py omits those formats from BLOCKED_ATTACHMENT_EXTENSIONS and BLOCKED_ATTACHMENT_MIME_TYPES, and helium/planner/serializers/attachmentserializer.py relies on those blocklists. An uploaded SVG served as image/svg+xml can execute embedded script when a visitor opens its public attachment URL, allowing persistent attacker-controlled active content and phishing under an application-managed storage URL. The attachment storage uses a separate origin from the application, so same-origin policy prevents the script from reading application cookies or storage, and application-session compromise is not supported by the maintained deployment configuration. This issue is fixed in version 2.2.60.
Weakness: CWE-79
Which versions are affected by CVE-2026-55876?
How do I fix CVE-2026-55876?
No fix has been published for CVE-2026-55876 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-55876 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55876 exists.
Sources
Also known as GHSA-7r65-76fw-ch5c.