Medium severity · published May 26, 2026
CVE-2026-44903
Prometheus: Stored XSS via crafted histogram bucket label values in the heatmap display of the old Prometheus web UI
6.1
CVSS
0.2%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 10% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
PR
prometheus · prometheus
>= 2.49.0, < 3.5.3; >= 3.6.0-rc.0, < 3.11.3 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-44903
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-44903
Patch
https://github.com/prometheus/prometheus/commit/38f23b9075ced1de2b82d2dad8b2bebb1ecd5b7d
Mitigation
https://github.com/prometheus/prometheus/security/advisories/GHSA-fw8g-cg8f-9j28
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