CVE-2026-44903
Analyzed Analyzed - Analysis Complete
Stored XSS in Prometheus Legacy Web UI Heatmap Chart

Publication date: 2026-05-26

Last updated on: 2026-06-05

Assigner: GitHub, Inc.

Description
Prometheus is an open-source monitoring system and time series database. From 2.49.0 to before 3.5.3 and 3.11.3, in the Prometheus server's legacy web UI (enabled via the command-line flag --enable-feature=old-ui), the histogram heatmap chart view does not escape le label values when inserting them into the HTML for use as axis tick mark labels. An attacker who can inject crafted metrics can execute JavaScript in the browser of any Prometheus user who views the metric in the heatmap chart UI. This vulnerability is fixed in 3.5.3 and 3.11.3.
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Meta Information
Published
2026-05-26
Last Modified
2026-06-05
Generated
2026-06-16
AI Q&A
2026-05-27
EPSS Evaluated
2026-06-14
NVD
CVE-2026-44903
Affected Vendors & Products
Showing 2 associated CPEs
Vendor Product Version / Range
prometheus prometheus From 3.6.0 (inc) to 3.11.3 (exc)
prometheus prometheus From 2.49.0 (inc) to 3.5.3 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
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Executive Summary

This vulnerability exists in the Prometheus monitoring system's legacy web UI, specifically in the histogram heatmap chart view. The issue is that label values are not properly escaped when inserted into the HTML for axis tick mark labels. As a result, an attacker who can inject specially crafted metrics can execute arbitrary JavaScript code in the browser of any user who views the affected heatmap chart UI.

This vulnerability affects Prometheus versions from 2.49.0 up to but not including 3.5.3 and 3.11.3, and it is fixed in versions 3.5.3 and 3.11.3.

Impact Analysis

The vulnerability allows an attacker to execute JavaScript code in the browser of any Prometheus user who views the compromised heatmap chart UI. This can lead to cross-site scripting (XSS) attacks, potentially resulting in unauthorized actions performed on behalf of the user, theft of sensitive information such as session tokens, or other malicious activities within the user's browser context.

Mitigation Strategies

To mitigate this vulnerability, upgrade your Prometheus server to version 3.5.3 or 3.11.3 or later, where the issue is fixed.

Alternatively, disable the legacy web UI by not enabling the --enable-feature=old-ui flag, as the vulnerability exists only in the legacy UI.

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