CVE-2026-40179: Prometheus: Stored XSS via metric names and label values in web UI tooltips and metrics explorer
Impact
Stored cross-site scripting (XSS) via crafted metric names in the Prometheus web UI:
Old React UI + New Mantine UI: When a user hovers over a chart tooltip on the Graph page, metric names containing HTML/JavaScript are injected into innerHTML without escaping, causing arbitrary script execution in the user's browser. Old React UI only: When a user opens the Metric Explorer (globe icon next to the PromQL expression input field), and a metric name containing HTML/JavaScript is rendered in the fuzzy search results, it is injected into innerHTML without escaping, causing arbitrary script execution in the user's browser. Old React UI only: When a user views a heatmap chart and hovers over a cell, the le label values of the underlying histogram buckets are interpolated into innerHTML without escaping. While le is conventionally a numeric bucket boundary, Prometheus does not enforce this — arbitrary UTF-8 strings are accepted as label values, allowing script injection via a crafted scrape target or remote write.
With Prometheus v3.x defaulting to UTF-8 metric and label name validation, characters like <, >, and " are now valid in metric names and labels, making this exploitable.
An attacker who can inject metrics (via a compromised scrape target, remote write, or OTLP receiver endpoint) can execute JavaScript in the browser of any Prometheus user who views the metric in the Graph UI. From the XSS context, an attacker could for example:
- Read /api/v1/status/config to extract sensitive configuration (although credentials / secrets are redacted by the server) - Call /-/quit to shut down Prometheus (only if --web.enable-lifecycle is set) - Call /api/v1/admin/tsdb/deleteseries to delete data (only if --web.enable-admin-api is set) - Exfiltrate metric data to an external server
Both the new Mantine UI and the old React UI are affected. The vulnerable code paths are:
- web/ui/mantine-ui/src/pages/query/uPlotChartHelpers.ts — tooltip innerHTML with unescaped labels.name - web/ui/react-app/src/pages/graph/GraphHelpers.ts — tooltip content with unescaped labels.name - web/ui/react-app/src/pages/graph/MetricsExplorer.tsx — fuzzy search results rendered via dangerouslySetInnerHTML without sanitization - web/ui/react-app/src/vendor/flot/jquery.flot.heatmap.js — heatmap tooltip with unescaped label values
Patches
A patch has been published in Prometheus 3.5.2 LTS and Prometheus 3.11.2. The fix applies escapeHTML() to all user-controlled values (metric names and label values) before inserting them into innerHTML. This advisory will be updated with the patched version once released.
Workarounds
- If using the remote write receiver (--web.enable-remote-write-receiver), ensure it is not exposed to untrusted sources. - If using the OTLP receiver (--web.enable-otlp-receiver), ensure it is not exposed to untrusted sources. - Ensure scrape targets are trusted and not under attacker control. - Do not enable admin / mutating API endpoints (e.g. --web.enable-admin-api or web.enable-lifecycle) in cases where you cannot prevent untrusted data from being ingested. - Users should avoid clicking untrusted links, especially those containing functions such as labelreplace, as they may generate poisoned label names and values.
Acknowledgements
Thanks to @gladiator9797 (Duc Anh Nguyen from TinyxLab) for reporting this.
Other sources
Prometheus is an open-source monitoring system and time series database. Versions 3.0 through 3.5.1 and 3.6.0 through 3.11.1 have stored cross-site scripting vulnerabilities in multiple components of the Prometheus web UI where metric names and label values are injected into innerHTML without escaping. In both the Mantine UI and old React UI, chart tooltips on the Graph page render metric names containing HTML/JavaScript without sanitization. In the old React UI, the Metric Explorer fuzzy search results use dangerouslySetInnerHTML without escaping, and heatmap cell tooltips interpolate le label values without sanitization. With Prometheus v3.x defaulting to UTF-8 metric and label name validation, characters like <, >, and " are now valid in metric names and labels. An attacker who can inject metrics via a compromised scrape target, remote write, or OTLP receiver endpoint can execute arbitrary JavaScript in the browser of any Prometheus user who views the metric in the Graph UI, potentially enabling configuration exfiltration, data deletion, or Prometheus shutdown depending on enabled flags. This issue has been fixed in versions 3.5.2 and 3.11.2. If developers are unable to immediately update, the following workarounds are recommended: ensure that the remote write receiver (--web.enable-remote-write-receiver) and the OTLP receiver (--web.enable-otlp-receiver) are not exposed to untrusted sources; verify that all scrape targets are trusted and not under attacker control; avoid enabling admin or mutating API endpoints (e.g., --web.enable-admin-api or --web.enable-lifecycle) in environments where untrusted data may be ingested; and refrain from clicking untrusted links, particularly those containing functions such as labelreplace, as they may generate poisoned label names and values.
— MITRE
Affected Software
Remediation
Patch Available
Event History
Frequently Asked Questions
What is the severity of CVE-2026-40179?
CVE-2026-40179 has a medium severity rating of 5.3.
How do I fix CVE-2026-40179?
To fix CVE-2026-40179, users should apply the patch available in the latest release of Prometheus.
What type of vulnerability is CVE-2026-40179?
CVE-2026-40179 is a Stored Cross-Site Scripting (XSS) vulnerability.
What is the impact of CVE-2026-40179?
The impact of CVE-2026-40179 allows an attacker to execute arbitrary JavaScript in the context of the user's browser through crafted metric names.
Which versions of Prometheus are affected by CVE-2026-40179?
CVE-2026-40179 affects the Prometheus web UI for both the old React UI and the new Mantine UI.