CVE-2026-33557 | Apache Kafka: Missing JWT token validation in OAUTHBEARER authentication

A possible security vulnerability has been identified in Apache Kafka. By default, the broker property `sasl.oauthbearer.jwt.validator.class` is set to `org.apache.kafka.common.security.oauthbearer.DefaultJwtValidator`. It accepts any JWT token without validating its signature, issuer, or audience. An attacker can generate a JWT token from any issuer with the `preferred_username` set to any user, and the broker will accept it. We advise the Kafka users using kafka v4.1.0 or v4.1.1 to set the config `sasl.oauthbearer.jwt.validator.class` to `org.apache.kafka.common.security.oauthbearer.BrokerJwtValidator` explicitly to avoid this vulnerability. Since Kafka v4.1.2 and v4.2.0 and later, the issue is fixed and will correctly validate the JWT token.

Published: 2026-04-20 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-33557 is rated Moderate Risk (50.2/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.50%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-33557

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.20% 0.50% +0.30%
2 2026-04-26 0.12% 0.20% +0.07%
3 2026-04-23 — 0.12% —

Full EPSS history (4 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33557

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.1 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
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:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 5.2 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-33557

GitHub Security Advisory for CVE-2026-33557

GHSA-28jg-cgg7-j4wc · Severity: critical · Ecosystem: maven — Apache Kafka does not validate JWT tokens in its OAUTHBEARER authentication implementation

OS Trackers for CVE-2026-33557

vendor priority summary link
ubuntu medium CVE-2026-33557 medium priority: Ubuntu including 1 source packages (kafka), 6 status rows across 6 suites (bionic, jammy, noble, questing, resolute, upstream): DNE 4, needs-triage 2. https://ubuntu.com/security/CVE-2026-33557

Affected software / configurations for CVE-2026-33557

Vendor Product Version Raw CPE
apache kafka >= 4.1.0, < 4.1.2 cpe:2.3:a:apache:kafka:*:*:*:*:*:*:*:*

References for CVE-2026-33557

cvelogic Threat Intelligence