EUVD-2026-36128
GHSA-2jcm-hq8r-84wx
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
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
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
6Blast Radius
ecosystem impact- 90 pypi packages depend on kafka-python (74 direct, 16 indirect)
Ecosystem-wide dependent count for version 2.3.2.
DescriptionCVE.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.
Articles & Coverage 2
AnalysisAI
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.
Technical ContextAI
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.
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.
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Same weakness CWE-400 – Uncontrolled Resource Consumption
View allSame technique Denial Of Service
View allVendor StatusVendor
SUSE
Severity: ImportantShare
External POC / Exploit Code
Leaving vuln.today