XSS in Prometheus
CVE-2026-44903
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (13.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 13.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000
Affected products
- Prometheus — versions >= 2.49.0, < 3.5.3, >= 3.6.0-rc.0, < 3.11.3
Weakness classification (CWE)
References
- github.com/prometheus/prometheus/security/advisories/GHSA-fw8g-cg8f-9j28 (Patch, Mitigation, Vendor Advisory)
- github.com/prometheus/prometheus/commit/38f23b9075ced1de2b82d2dad8b2bebb1ecd5b7d (Patch)
Frequently asked questions
- What is CVE-2026-44903?
- CVE-2026-44903 is a medium-severity vulnerability in Prometheus, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-05-26.
- How severe is CVE-2026-44903?
- Medium severity. CVSS v3 base score is 6.1 out of 10.