Cyber Resilience

CVE-2026-33557

Auth Bypass in Apache Kafka 4.1.0 – 4.1.2

Auth Bypass
Published
20 April 2026
Modified
15 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 9.1
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS Score 0.0068 49th percentile
Risk Priority 68 floored blend · peak EPSS

Summary

CVE-2026-33557 is a critical-severity Improper Validation of Specified Index, Position, or Offset in Input (CWE-1285) vulnerability in Apache Kafka. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 49th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-33557 is a high-severity vulnerability (CVSS 3.1 score of 9.1) in Apache Kafka, stemming from the default broker property `sasl.oauthbearer.jwt.validator.class` being set to `org.apache.kafka.common.security.oauthbearer.DefaultJwtValidator`. This validator accepts any JSON Web Token (JWT) without verifying its signature, issuer, or audience, allowing improper authentication. The issue affects Apache Kafka versions 4.1.0 and 4.1.1.

A remote attacker with network access to the Kafka broker can exploit this vulnerability without privileges or user interaction by generating a custom JWT token from any issuer, setting the `preferred_username` claim to impersonate any valid user. Successful exploitation enables high confidentiality and integrity impacts, such as unauthorized access to topics, data exfiltration, or message injection, corresponding to CWE-1285 (Improper Validation of Specified Index or Position).

Apache Kafka advisories recommend that users of versions 4.1.0 and 4.1.1 explicitly configure `sasl.oauthbearer.jwt.validator.class` to `org.apache.kafka.common.security.oauthbearer.BrokerJwtValidator` as a mitigation. The vulnerability is fixed in Kafka 4.1.2, 4.2.0, and later releases, where JWT validation is properly enforced. Additional details are available in the official Kafka CVE list at https://kafka.apache.org/cve-list and related mailing list announcements.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

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…

more

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.

CWE(s)
CWE-1285CWE-303

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1133 External Remote Services Persistence
Adversaries may leverage external-facing remote services to initially access and/or persist within a network.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-56128Same product: Apache Kafka
CVE-2025-27819Same product: Apache Kafka
CVE-2025-27818Same product: Apache Kafka
CVE-2024-27309Same product: Apache Kafka
CVE-2025-27817Same product: Apache Kafka
CVE-2026-41115Same product: Apache Kafka
CVE-2024-31141Same product: Apache Kafka
CVE-2026-33558Same product: Apache Kafka
CVE-2026-43868Same vendor: Apache
CVE-2026-45811Same vendor: Apache

Affected Assets

apache
kafka
4.1.0 — 4.1.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.4.2
  • V2.1.1
  • V2.2.1
  • V2.2.2

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation at post-design stages directly uncovers incorrect implementations of required authentication algorithms.

SI-10 Information Input Validation good match

Requires explicit validation of supplied indices/offsets/positions before they are used to access buffers or other indexable resources.

SA-15 Development Process, Standards, and Tools partial match

Requiring documented development processes, standards, and tools reduces the chance that an established authentication algorithm is coded incorrectly.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require input validation, preventing this class of flaw at development time.

ID.RA-01 partial match
prevents

Vulnerability identification processes can discover missing index validation via scanning or reviews.

PR.PS-02 partial match
prevents

Patching and replacement can remediate instances of the weakness after discovery.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.5 Secure authentication full match
degrades

Secure authentication control directly requires correct implementation of authentication algorithms.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect missing or incorrect index validation during development and acceptance.

A.8.24 Use of cryptography partial match
degrades

Cryptography control addresses proper use of authentication algorithms but is broader than authentication alone.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle includes input validation requirements that can prevent improper index handling.

A.8.26 Application security requirements partial match
prevents

Application security requirements typically mandate bounds checking and validation of offsets/indices.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include defensive input validation and bounds checking for indexable resources.

References