CVE-2026-44903
MediumCVSS 6.1Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
Prometheus from version 2.49.0 to before 3.5.3 and 3.11.3 contains an XSS vulnerability in the legacy web UI (enabled via --enable-feature=old-ui). In the histogram heatmap chart view, 'le' label values are not properly escaped, allowing an attacker to inject JavaScript via crafted metrics.
Risk Assessment
JavaScript execution in a Prometheus user's browser could lead to session theft and unauthorized access to monitoring data.
Recommendation
Update Prometheus to version 3.5.3 or 3.11.3 and consider disabling the legacy UI.
Other vulnerabilities in Prometheus
See all- CVE-2026-42154High
Prometheus before versions 3.5.3 and 3.11.3 does not validate the declared decoded length in a snappy-compressed request to the /api/v1/read endpoint before allocating memory. An unauthenticated attacker can send a small payload causing a huge heap allocation, potentially exhausting memory and crashing the Prometheus process under concurrent load.
- CVE-2026-42151High
Prometheus prior to versions 3.5.3 and 3.11.3 stores the client_secret field in Azure AD OAuth configuration as a plain string instead of a Secret. This exposes the Azure OAuth client secret in plaintext to any user or process with access to the /-/config endpoint.
Original NVD description (English source)
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.