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GHSA-fw8g-cg8f-9j28

MEDIUM

GHSA-fw8g-cg8f-9j28 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in github.com/prometheus/prometheus. O3 Security confirms whether GHSA-fw8g-cg8f-9j28 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Prometheus vulnerable to stored XSS via crafted histogram bucket label values in the old web UI heatmap display

Also known asBIT-prometheus-2026-44903CVE-2026-44903GO-2026-5381
Published
May 5, 2026
Updated
Jun 25, 2026
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed

Blast Radius

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
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/prometheus/prometheusall versions0.311.3

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/prometheus/prometheus. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. 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 GHSA-fw8g-cg8f-9j28 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether GHSA-fw8g-cg8f-9j28 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to GHSA-fw8g-cg8f-9j28. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

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
O3 Security · Impact-Aware SCA

Is GHSA-fw8g-cg8f-9j28 in your dependencies?

O3 detects GHSA-fw8g-cg8f-9j28 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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