CVE-2026-44903 Prometheus: Stored XSS via crafted histogram bucket label values in the heatmap display of the old Prometheus web UI
Attackers can execute JavaScript in Prometheus users' browsers via crafted histogram labels in the legacy web UI, requiring the old-ui feature flag.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-44903?
CVE-2026-44903 is a medium-severity cross-site scripting vulnerability in prometheus, published on 26 May 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2026-44903?
4 open source packages ship an affected version, including github.com/prometheus/prometheus and prometheus. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/prometheus/prometheus Go | All versions | 0.311.3 |
github.com/prometheus/prometheus Go | All versions | 0.311.3 |
github.com/prometheus/prometheus Go | All versions | 0.311.3 |
prometheus Bitnami | All versions | 0.305.3, 0.311.3, 3.5.3, 3.11.3 |
Products include Prometheus Prometheus.
How do I fix CVE-2026-44903?
Upgrade github.com/prometheus/prometheus to 0.311.3 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-44903 being exploited?
There is no known exploitation of CVE-2026-44903 in the wild and no public exploit code.
Other vulnerabilities in prometheus
- CVE-2026-42151 Prometheus Azure AD remote write OAuth client secret exposed via config API
- CVE-2026-42154 Prometheus: remote read endpoint allows denial of service via crafted snappy payload
- CVE-2021-29622 Arbitrary redirects under /new endpoint
- CVE-2019-3826 Cross-site scripting in prometheus
- CVE-2026-40179 Prometheus: Stored XSS via metric names and label values in web UI tooltips and metrics explorer
Sources
Also known as BIT-prometheus-2026-44903, CLEANSTART-2026-CD57328, CLEANSTART-2026-DS50998, CLEANSTART-2026-GK28473, CLEANSTART-2026-KD10786, CLEANSTART-2026-PY51486 and 135 more.