How severe is CVE-2026-44903?

No CVSS score has been assigned to CVE-2026-44903 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-44903?

CVE-2026-44903 affects the following packages: github.com/prometheus/prometheus (Go). Ecosystems affected: Go.

How do I fix CVE-2026-44903?

Update github.com/prometheus/prometheus to 0.311.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44903 is resolved across your whole dependency graph.

How do I detect CVE-2026-44903 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/prometheus/prometheus, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-44903 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2026-44903 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-44903 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-44903?

CVE-2026-44903 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 10th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-44903?

CVE-2026-44903 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-44903 published, and has it been updated?

CVE-2026-44903 was published on May 26, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

CVE-2026-44903 — prometheus

Fix: prometheus/prometheus@38f23b9

CVE-2026-44903 is a Cross-site Scripting (XSS) vulnerability in github.com/prometheus/prometheus. A fix is available for github.com/prometheus/prometheus — see the affected versions and patch details below.

Prometheus: Stored XSS via crafted histogram bucket label values in the heatmap display of the old Prometheus web UI

Also known asBIT-prometheus-2026-44903GHSA-fw8g-cg8f-9j28GO-2026-5381

Published

May 26, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-44903.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs10th percentile — riskier than 10% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐹github.com/prometheus/prometheus

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

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 (e.g. via a compromised scrape target, remote write, or OTLP receiver endpoint) can execute JavaScript in the browser of any Prometheus user who views the metric in the heatmap chart UI. From the XSS context, an attacker could for example:

Read /api/v1/status/config to extract sensitive configuration (although credentials / secrets are redacted by the server)
Call /-/quit to shut down Prometheus (only if --web.enable-lifecycle is set)
Call /api/v1/admin/tsdb/delete_series to delete data (only if --web.enable-admin-api is set)
Exfiltrate metric data to an external server

Note that this only affects users who have explicitly enabled the legacy Prometheus web UI using the --enable-feature=old-ui command-line flag.

Patches

https://github.com/prometheus/prometheus/commit/38f23b9075ced1de2b82d2dad8b2bebb1ecd5b7d

Workarounds

If at all possible, disable the legacy web UI by removing the --enable-feature=old-ui command-line flag).

If this is not an option, take the following precautions:

If using the remote write receiver (--web.enable-remote-write-receiver), ensure it is not exposed to untrusted sources.
If using the OTLP receiver (--web.enable-otlp-receiver), ensure it is not exposed to untrusted sources.
Ensure scrape targets are trusted and not under attacker control.
Do not enable admin / mutating API endpoints (e.g. --web.enable-admin-api or web.enable-lifecycle) in cases where you cannot prevent untrusted data from being ingested.
Users should avoid clicking untrusted links, especially those containing functions such as label_replace, as they may generate poisoned label names and values.

References

CVE-2019-10215 — prior stored DOM XSS vulnerability in Prometheus query history, fixed in v2.7.2
CVE-2026-40179 — prior stored DOM XSS vulnerability in Prometheus web UI (hover tooltips and metrics explorer), fixed in v3.11.2

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/prometheus/prometheus`	all versions	0.311.3`go get github.com/prometheus/prometheus@v0.311.3`

Affected Products

1 product · 2 configurations

Application

prometheusprometheus

≥ 3.6.0 && < 3.11.3

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/prometheus/prometheus, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/prometheus/prometheus to 0.311.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44903 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### Impact 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 (e.g. via a compromised scrape target, remote write, or OTLP receiver endpoint) can execute JavaScript in the browser of any Prometheus user who views the metric in the heatmap chart UI. From the XSS context, an attacker could for example: - Read `/api/v1/status/config` to extract sensitive configuratio