Incorrect Implementation of Authentication Algorithm in Apache Kafka's SCRAM implementation.
Issue Summary:
Apache Kafka's implementation of the Salted Challenge Response Authentication Mechanism (SCRAM) did not fully adhere to the requirements of RFC 5802 [1].
Specifically, as per RFC 5802, the server must verify that the nonce sent by the client in the second message matches the nonce sent by the server in its first message.
However, Kafka's SCRAM implementation did not perform this validation.
Impact:
This vulnerability is exploitable only when an attacker has plaintext access to the SCRAM authentication exchange. However, the usage of SCRAM over plaintext is strongly
discouraged as it is considered an insecure practice [2]. Apache Kafka recommends deploying SCRAM exclusively with TLS encryption to protect SCRAM exchanges from interception [3].
Deployments using SCRAM with TLS are not affected by this issue.
How to Detect If You Are Impacted:
If your deployment uses SCRAM authentication over plaintext communication channels (without TLS encryption), you are likely impacted.
To check if TLS is enabled, review your server.properties configuration file for listeners property. If you have SASL_PLAINTEXT in the listeners, then you are likely impacted.
Fix Details:
The issue has been addressed by introducing nonce verification in the final message of the SCRAM authentication exchange to ensure compliance with RFC 5802.
Affected Versions:
Apache Kafka versions 0.10.2.0 through 3.9.0, excluding the fixed versions below.
Fixed Versions:
3.9.0
3.8.1
3.7.2
Users are advised to upgrade to 3.7.2 or later to mitigate this issue.
Recommendations for Mitigation:
Users unable to upgrade to the fixed versions can mitigate the issue by:
- Using TLS with SCRAM Authentication:
Always deploy SCRAM over TLS to encrypt authentication exchanges and protect against interception.
- Considering Alternative Authentication Mechanisms:
Evaluate alternative authentication mechanisms, such as PLAIN, Kerberos or OAuth with TLS, which provide additional layers of security.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (5.3): severity, escalated by confirmed exploitation. This CVE's 5.3 is its impact severity (EG Severity), not escalated.
- EG Severity
- 5.3 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.8% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-31). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it