Cross-Site Scripting (XSS) in nicegui (CVE-2026-25516)
Summary
Cross-site scripting in nicegui (CVE-2026-25516). Risk of unauthorized operations or information disclosure. Exploitable via markdown2. Mitigation: upgrade to 3.7.0 or later.
Original description
The description as published by the source.
Description
The ui.markdown() component uses the markdown2 library to convert markdown content to HTML, which is then rendered via innerHTML. By default, markdown2 allows raw HTML to pass through unchanged. This means that if an application renders user-controlled content through ui.markdown(), an attacker can inject malicious HTML containing JavaScript event handlers.
Unlike other NiceGUI components that render HTML (ui.html(), ui.chat_message(), ui.interactive_image()), the ui.markdown() component does not provide or require a sanitize parameter, leaving applications vulnerable to XSS attacks.
Proof of Concept
from nicegui import ui
# User-controlled input containing malicious payload
user_input = 'Hello! '
ui.markdown(user_input) # XSS executes when page loads
ui.run()
When this page loads, the JavaScript in the onerror handler executes, potentially allowing an attacker to:
- Steal session cookies or authentication tokens
- Perform actions on behalf of the user
- Redirect users to malicious sites
- Modify page content
Impact
Applications that render user-provided content through ui.markdown() are vulnerable to stored or reflected XSS attacks. This is particularly concerning for:
- Chat applications displaying user messages
- CMS or documentation systems with user-editable content
- Any application that displays markdown from untrusted sources
Remediation
A release has been published in version 3.7.0.
For U…
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
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-2026-25516 has been found in nicegui.
Attackers can target a specific entry point like markdown2 over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade nicegui to 3.7.0 or later.
If unsure, ask your IT team or search "nicegui CVE-2026-25516" on the vendor's site.
CVE-2026-25516 (nicegui) — CWE-79
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: markdown2 / innerHTML / sanitize / onerror
Patched: 3.7.0 — apply immediately
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 nicegui. Attackers reach the vulnerable code path via markdown2 without authentication.
Check the vendor advisory for the affected versions of nicegui. Attack surface: markdown2 / innerHTML / sanitize / onerror.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 3.7.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'nicegui' . 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 'nicegui' . | 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
niceguiを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade nicegui to 3.7.0ステージング環境で 3.7.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in production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。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com