CVE-2026-44903: Prometheus: Stored XSS via crafted histogram bucket label values in the heatmap display of the old Prometheus web UI
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.5.3 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 3.11.3
Event History
Frequently Asked Questions
What is the severity of CVE-2026-44903?
CVE-2026-44903 has a risk score of 33, indicating a moderate vulnerability.
How do I fix CVE-2026-44903?
To mitigate CVE-2026-44903, upgrade to Prometheus version 3.5.3 or 3.11.3 and disable the legacy web UI option.
What is the impact of CVE-2026-44903 on Prometheus?
CVE-2026-44903 allows for stored XSS attacks via crafted histogram bucket label values in the legacy web UI.
Which versions of Prometheus are affected by CVE-2026-44903?
CVE-2026-44903 impacts Prometheus versions from 2.49.0 to before 3.5.3 and 3.11.3.
What feature must be enabled to exploit CVE-2026-44903?
To exploit CVE-2026-44903, the legacy web UI feature must be enabled using the command-line flag --enable-feature=old-ui.