Cross-Site Scripting (XSS) in Helium (CVE-2026-55876)
Summary
Cross-site scripting in Helium (CVE-2026-55876). Risk of unauthorized operations or information disclosure. Exploitable via POST /planner/attachments/.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-55876 has been found in Helium.
Attackers can target a specific entry point like POST /planner/attachments/ over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 3.5/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Helium CVE-2026-55876" on the vendor's site.
CVE-2026-55876 (Helium) — CWE-79 / CVSS v3 3.5
Attack vector: remote (network-reachable)
Attack surface: POST /planner/attachments/
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Cross-site scripting (XSS) (CWE-79) exists in Helium. Attackers reach the vulnerable code path via POST /planner/attachments/.
Check the vendor advisory for the affected versions of Helium. Attack surface: POST /planner/attachments/.
Severity: Low (CVSS 3.5/10). Risk of unauthorized operations or information disclosure.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual POST /planner/attachments/ requests with malformed payloads or SQL meta-characters. Run grep -r 'Helium' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'Helium' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
Heliumを grep し、稼働しているサービス・バージョンを把握する。 -
2Hunt for indicators of compromise detect
grep 'POST /planner/attachments/' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
POST /planner/attachments/への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Post-deployment verification verify
Replay attack against POST /planner/attachments/ on staging to confirm patch closes the vectorパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番では Step 2 と同じログクエリでアラート再発が無いか継続監視。