Security readout for executives and security teams
Plain-English summary
Apache Kafka could accept a forged login token when using the affected OAUTHBEARER configuration. In affected versions, the default validator did not verify the token signature, issuer, or audience, so a remote attacker could impersonate a Kafka user. This is critical because it threatens data confidentiality and integrity in Kafka-backed systems.
Executive priority
Treat this as urgent for any Kafka environment using OAUTHBEARER on affected versions. The risk is unauthorized identity impersonation, which can compromise sensitive event streams and business workflows. Patch or apply the Apache-recommended validator configuration promptly.
Technical view
Kafka 4.1.0 and 4.1.1 are described as vulnerable when sasl.oauthbearer.jwt.validator.class uses DefaultJwtValidator. That validator accepts JWTs without validating signature, issuer, or audience, allowing preferred_username impersonation. Apache advises BrokerJwtValidator for affected 4.1.x deployments; Kafka 4.1.2 and 4.2.0 and later fix validation.
Likely exposure
Most likely exposure is Kafka brokers running 4.1.0 or 4.1.1 with OAUTHBEARER authentication and the default JWT validator. Systems not using OAUTHBEARER, not running affected versions, or already configured with BrokerJwtValidator are less likely exposed based on the provided sources.
Exploitation context
The CVSS vector indicates network reachability, low complexity, no privileges, and no user interaction. The provided bundle marks KEV as false and does not cite active exploitation. Public evidence here supports exploitability in principle, not confirmed exploitation in the wild.
Researcher notes
Evidence is strong for the default validation flaw and vendor-stated remediation. The source bundle is incomplete on product packaging impact beyond Apache Kafka itself. Do not assume downstream distributions are affected or fixed without checking their advisories.
Mitigation direction
- Upgrade affected Kafka deployments to 4.1.2, 4.2.0, or later.
- On Kafka 4.1.0 or 4.1.1, explicitly configure BrokerJwtValidator.
- Prioritize internet-exposed or shared Kafka clusters first.
- Review Apache Kafka guidance before applying environment-specific changes.
Validation and detection
- Inventory Kafka broker versions across all environments.
- Check whether OAUTHBEARER authentication is enabled on broker listeners.
- Verify sasl.oauthbearer.jwt.validator.class is not DefaultJwtValidator on affected versions.
- Confirm upgraded clusters run Kafka 4.1.2, 4.2.0, or later.
- Review authentication logs for unexpected preferred_username usage.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-1285: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCWE-303: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCredential and access behavior lookup
The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-33557 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
2 official scoresWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N3.95.2CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L3.94.7redhat-SADPVulnerability scoring details
Base CVSS 3.1 score
9.1CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Base CVSS 3.1 score
8.6HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- ADP timelineredhat-SADP
Made public.
- CVE publishedCVE Program
The CVE record was published.
- ADP timelineredhat-SADP
Reported to Red Hat.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2026-04-20T14:01:07.601Z: Reported to Red Hat.
- 2026-04-20T13:28:43.669Z: Made public.
Source materials
- CVE List V5 sourceCVE List V5
- https://kafka.apache.org/cve-listCVE reference, apache · vendor-advisory
- https://lists.apache.org/thread/v57o00hm6yszdpdnvqx2ss4561yh953hCVE reference, apache · mailing-list
- https://access.redhat.com/security/cve/CVE-2026-33557CVE reference, redhat-SADP · vdb-entry, x_refsource_REDHAT
- RHBZ#2459739CVE reference, redhat-SADP · issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33557.jsonCVE reference, redhat-SADP · x_sadp-csaf-vex
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Validation of Specified Index, Position, or Offset in Input
Improper Validation of Specified Index, Position, or Offset in Input represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Incorrect Implementation of Authentication Algorithm
Incorrect Implementation of Authentication Algorithm represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.