CVE-2026-40557 [Medium] | Security Vulnerability in Storm Prometheus Reporter

Improper Certificate Validation via Global SSL Context Downgrade in Apache Storm Prometheus Reporter Versions Affected: from 2.6.3 to 2.8.6 Description: In production deployments where an administrator enables storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation (by default it is disabled) intending to affect only the Prometheus reporter, the undocumented global side effect creates an attack surface across every TLS-protected communication channel in the Storm daemon. The PrometheusPreparableReporter class implements an INSECURE_TRUST_MANAGER that accepts all SSL certificates without validation, with empty checkClientTrusted and checkServerTrusted methods. Most critically, when the storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation configuration option is enabled (default = disabled) for HTTPS Prometheus PushGateway connections, the INSECURE_CONNECTION_FACTORY calls SSLContext.setDefault(sslContext), which globally replaces the JVM's default SSL context rather than applying the insecure context only to the Prometheus connection. This payload flows through storm.yaml configuration → PrometheusPreparableReporter.prepare() → INSECURE_CONNECTION_FACTORY → SSLContext.setDefault(), resulting in a JVM-wide TLS security downgrade. All subsequent HTTPS connections in the process - including ZooKeeper, Thrift, Netty, and UI connections - silently trust all certificates, including self-signed, expired, and attacker-generated ones, enabling man-in-the-middle interception of cluster state, topology submissions, tuple data, and administrative credentials. Mitigation: 2.x users should upgrade to 2.8.7 if the Prometheus Metrics Reporter is used. Prometheus Metrics Reporter Users who cannot upgrade immediately should remove the storm.daemon.metrics.reporter.plugin.prometheus.skip_tls_validation: true setting from their storm.yaml configuration and instead configure a proper truststore containing the PushGateway's certificate.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-06	0.01%	0.10%	+0.09%
2	2026-04-28	—	0.01%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-06

0.01%

0.10%

+0.09%

2026-04-28

—

0.01%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
4.8	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:L) Some sensitive info could get out, but not a total data dump. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.	2.2	2.5	134c704f-9b21-4f2e-91b3-4a467353bcc0

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

4.8

3.1

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L): Some sensitive info could get out, but not a total data dump.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N): Service keeps running; no real outage angle.

2.2

2.5

134c704f-9b21-4f2e-91b3-4a467353bcc0

Affected software / configurations for CVE-2026-40557

Vendor	Product	Version	Raw CPE
apache	storm_prometheus_reporter	>= 2.6.3, < 2.8.7	cpe:2.3:a:apache:storm_prometheus_reporter::::::::

References for CVE-2026-40557

URL	Tags
https://lists.apache.org/thread/f5bv68z1y5xstz22psjk05p3wn86knjq	Mailing List Vendor Advisory
http://www.openwall.com/lists/oss-security/2026/04/25/2	Mailing List Third Party Advisory

URL

CVE-2026-40557 | Apache Storm Prometheus Reporter: Disabling TLS verification for Prometheus Reporter also disables it for all other connections

Exploit prediction scoring system (EPSS) score for CVE-2026-40557

Common vulnerability scoring system (CVSS) metrics for CVE-2026-40557

Weakness enumeration for CVE-2026-40557

GitHub Security Advisory for CVE-2026-40557

Affected software / configurations for CVE-2026-40557

References for CVE-2026-40557