EUVD-2026-36128
GHSA-2jcm-hq8r-84wx
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessPosition rogue/MITM Kafka broker
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DeliveryClient opens SASL SCRAM connection
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ExploitBroker returns huge PBKDF2 iteration count
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ExecutionClient calls hashlib.pbkdf2_hmac on event loop
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PersistCPU-bound hash blocks all I/O callbacks
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ImpactHeartbeats miss, consumer evicted, reconnect loop
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V2 - Validation and Business Logic Resource consumption limits
MITRE ATT&CK
1 technique across 1 tactic: Impact The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Exploitation requires the client to initiate a SASL SCRAM-SHA-256 or SCRAM-SHA-512 handshake against an attacker-controlled or MITM-intercepted broker endpoint - clients using PLAIN, GSSAPI/Kerberos, OAUTHBEARER, or no SASL at all are not on this code path. The attacker does not need credentials, user interaction, or any prior foothold on the client, but they must be able to deliver a forged server-first-message, which in practice means either operating a rogue broker the client is configured to reach (e.g. via a poisoned bootstrap.servers list, DNS hijack, or ARP spoof on the broker network) or breaking TLS trust when SASL_SSL is in use. Impact is limited to availability: the client process freezes its event loop and disconnects, but no data is read, written, or leaked, and the stall ends when the process is restarted. |
| Impact | The CVSS 4.0 vector AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N correctly captures a high-availability-only impact reachable without authentication or user interaction, yielding the 8.7 score; confidentiality and integrity are untouched because the malicious broker never completes the SCRAM exchange and gains no key material. The realistic prerequisite is non-trivial, however: the attacker must either operate a rogue broker that the client willingly connects to, or be positioned to MITM the bootstrap connection - which usually means TLS is disabled or trust is misconfigured, since SCRAM is typically tunnelled over SASL_SSL. There is no CISA KEV listing and no EPSS score was provided, and no public exploit identified at time of analysis, so this is best treated as a credible supply-chain/MITM hardening fix rather than an actively exploited issue; the impact when triggered is real, though - full client-loop stall affecting producers, consumers, admin, and heartbeats simultaneously. |
| Exploit ScenarioDerived | An attacker who can intercept the TCP handshake to the Kafka bootstrap broker (untrusted network, compromised DNS, or rogue broker advertised via a misconfigured listener) terminates the SCRAM handshake with a server-first-message containing an iteration count in the billions. The kafka-python client calls hashlib.pbkdf2_hmac() with that count on its main event loop thread and hangs indefinitely, stalling producer sends, consumer polls, admin operations, and heartbeats until the consumer is evicted from its group. No public PoC is referenced, but the fix diff makes the trigger straightforward to reconstruct. |
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Alert meAnalysisAIv3 – Jun 10, 2026
Denial of service in kafka-python versions prior to 2.3.2 allows a malicious or man-in-the-middle Kafka broker to freeze the client's event loop during SCRAM authentication by returning an excessive PBKDF2 iteration count. Because ScramClient.process_server_first_message() forwards the broker-supplied value directly to hashlib.pbkdf2_hmac() without bounds checking, producers, consumers, admin clients, and group heartbeats all stall, leading to consumer-group eviction and reconnect loops. No public exploit identified at time of analysis, though VulnCheck has published a vendor-style advisory and an upstream patch has been merged.
Earlier versions of this analysis (2)
Denial-of-service in kafka-python versions prior to 2.3.2 lets a malicious or man-in-the-middle Kafka broker freeze a client's event loop during SCRAM authentication by returning an excessively large PBKDF2 iteration count, halting producer sends, consumer polls, admin operations, and heartbeats. The flaw was reported by VulnCheck, a vendor patch is available, and no public exploit identified at time of analysis; CVSS 4.0 rates it 8.7 due to high availability impact with no authentication or user interaction required.
Denial of service in kafka-python versions prior to 2.3.2 lets a malicious or machine-in-the-middle Kafka broker freeze the Python client's event loop during SCRAM authentication by returning an excessively large PBKDF2 iteration count. The unvalidated value is fed directly into hashlib.pbkdf2_hmac(), stalling producers, consumers, admin clients, and heartbeats, with no public exploit identified at time of analysis.
RemediationAI
Vendor-released patch: upgrade kafka-python to 2.3.2 or later, which adds an explicit upper bound on the broker-supplied SCRAM iteration count before invoking hashlib.pbkdf2_hmac() and also introduces a receive_message_max_bytes frame-size guard (commit 6e4831444f972d169cdd11f5c8d50333cea3f19b and PRs https://github.com/dpkp/kafka-python/pull/3019 and https://github.com/dpkp/kafka-python/pull/3026). Where an immediate upgrade is not possible, restrict clients to known-good brokers by pinning bootstrap_servers to internal addresses and enforcing SASL_SSL with hostname verification and a private CA so a rogue or MITM broker cannot present itself - the trade-off is operational, requiring strict certificate and DNS hygiene. As a defense-in-depth measure, run the SCRAM-authenticating client in a dedicated process or thread pool so a stalled PBKDF2 call cannot block unrelated event loops, accepting the added complexity and slight latency.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in pypi
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
kafka-python is a pure-Python Apache Kafka client library (cpe:2.3:a:dana_powers:kafka-python) used to build producers, consumers, and admin tooling against Kafka brokers. SCRAM (Salted Challenge Response Authentication Mechanism, RFC 5802) negotiates a session key by having the client run PBKDF2-HMAC over the password using a salt and iteration count advertised by the server in the server-first-message. The library implements that step in kafka/scram.py, where the iteration count parsed from the broker frame is trusted and passed straight into hashlib.pbkdf2_hmac(), a synchronous, CPU-bound C routine that scales linearly with the iteration count. This is a classic CWE-400 Uncontrolled Resource Consumption: an unvalidated external value drives an unbounded amount of work on a single thread, blocking the asyncio/selector loop that also drives I/O, fetch, heartbeat, and timer callbacks.
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Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Network-reachable and unauthenticated, but requires attacker to control or MITM the broker connection (AC:H); only availability is impacted via event-loop stall.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
3DescriptionCVE.org
kafka-python prior to 2.3.2 contains a denial-of-service vulnerability in SCRAM authentication handling that allows a malicious or machine-in-the-middle broker to freeze the client event loop by supplying an excessively large iteration count. In scram.py, ScramClient.process_server_first_message() passes the broker-controlled SCRAM iteration count directly to hashlib.pbkdf2_hmac() without validation, blocking producer sends, consumer polls, admin operations, and heartbeats, which can cause consumer group eviction and repeated reconnect failures.
Blast Radius
ecosystem impact- 2 pypi packages depend on kafka-python (2 direct, 0 indirect)
Ecosystem-wide dependent count for version 2.3.2.
Articles & Coverage 2
Executive ViewAI
kafka-python versions before 2.3.2 contain a denial-of-service vulnerability triggered during SCRAM authentication that freezes client event loops; no public exploit identified at time of analysis. This impacts all client types (producers, consumers, admin tools) and directly threatens the availability and reliability of message-driven architectures and data pipelines. With a vendor patch available, organizations should prioritize upgrading to kafka-python 2.3.2+ within 30 days to eliminate this application-layer availability risk.
Apply vendor patch: kafka-python 2.3.2 or later.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
VulDB
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
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