{"id":"CVE-2026-111073","kind":"vulnerability","aliases":["CVE-2026-111073"],"related":[],"title":"Apache Kafka: telemetry push lets a client exhaust broker heap","description":"The broker-side PushTelemetry API (KIP-714) validates only the compressed size of a client's metrics payload against telemetry.max.bytes (default 1 MB) before decompressing it. ClientTelemetryUtils.decompress() then decompresses the payload with no limit on the decompressed output size, growing a heap buffer until the compressed input is exhausted. A small, highly compressible payload (for example gzip-compressed zeros) can therefore expand to hundreds of megabytes of broker heap.\n\n\nImpact:\n\n\nAn authenticated client can send a PushTelemetry request with a small compressed payload that decompresses to a very large size, consuming broker heap out of proportion to the request size. Repeated or concurrent requests can exhaust the broker heap and cause an OutOfMemoryError, degrading or crashing the broker; a client that targets multiple brokers can affect cluster availability. PushTelemetry is available to any authenticated client and is not gated by an ACL.\n\n\nMitigation:\n\n\nUpgrade to Apache Kafka 4.2.2, 4.3.1, or 4.4.0. On affected versions there is no configuration that fully prevents the amplification, because telemetry.max.bytes bounds only the compressed size; lowering telemetry.max.bytes reduces the worst-case decompressed size proportionally and is a partial mitigation.\n\n\nResolution:\n\n\n- From Apache Kafka 4.2.2, 4.3.1, and 4.4.0: ClientTelemetryUtils.decompress() enforces a maximum decompressed size equal to telemetry.max.bytes (default 1 MB). Decompression reads in bounded chunks and aborts with a TelemetryTooLargeException once the decompressed total exceeds the limit, so an over-large or highly compressible payload is rejected instead of being fully expanded in heap. The decompressed size is therefore bounded by default.","summary":"The broker's PushTelemetry API checks only the compressed size of client metrics before decompressing them with no output limit. An authenticated client can send a small, highly compressible payload that expands to hundreds of megabytes and causes OutOfMemoryError on the broker.","severity":"medium","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["kafka","kafka-brokers","kubernetes","package","self-hosted"],"not_affected_if":["fixed-version","no-untrusted-clients"],"how_to_check":"- Run `kafka-topics.sh --version` or check the Kafka version in the broker's build or package manifest, then compare against the fixed releases listed in Fix.\n- Check whether `telemetry.max.bytes` is set in `server.properties`; the default is 1 MB, and the sources say it bounds only the compressed size on affected versions.","fix":"- Upgrade Apache Kafka to `4.2.2`, `4.3.1`, or `4.4.0`, which enforce a decompressed size limit equal to `telemetry.max.bytes` and abort oversized payloads with TelemetryTooLargeException.\n- On affected versions, lowering `telemetry.max.bytes` is only a partial mitigation, since it reduces the worst-case expansion proportionally and does not fully prevent it.","status":"open","published_at":"2026-10-28T17:17:38+00:00","first_seen_at":"2026-10-28T17:34:08+00:00","triaged_at":"2026-10-28T17:35:11+00:00","updated_at":"2026-10-28T17:35:11+00:00","category":"package","confidence":0.8,"triage":{"at":"2026-10-28T17:35:11Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade Apache Kafka to `4.2.2`, `4.3.1`, or `4.4.0`, which enforce a decompressed size limit equal to `telemetry.max.bytes` and abort oversized payloads with TelemetryTooLargeException.\n- On affected versions, lowering `telemetry.max.bytes` is only a partial mitigation, since it reduces the worst-case expansion proportionally and does not fully prevent it.","reach":"network","title":"Apache Kafka: telemetry push lets a client exhaust broker heap","impact":"medium","summary":"The broker's PushTelemetry API checks only the compressed size of client metrics before decompressing them with no output limit. An authenticated client can send a small, highly compressible payload that expands to hundreds of megabytes and causes OutOfMemoryError on the broker.","category":"package","nicknames":[],"who_cares":["kafka","kafka-brokers","self-hosted","kubernetes"],"confidence":0.8,"needs_auth":"yes","worst_case":"Broker runs out of heap and crashes, degrading cluster availability","analyst_note":"","how_to_check":"- Run `kafka-topics.sh --version` or check the Kafka version in the broker's build or package manifest, then compare against the fixed releases listed in Fix.\n- Check whether `telemetry.max.bytes` is set in `server.properties`; the default is 1 MB, and the sources say it bounds only the compressed size on affected versions.","needs_analyst":false,"not_affected_if":["fixed-version","no-untrusted-clients"],"who_is_affected":"Any cluster running an affected Apache Kafka broker version is exposed, because PushTelemetry (KIP-714) is reachable by any authenticated client and is not gated by an ACL. Clusters where clients are fully trusted carry less practical risk, but an authenticated client that targets multiple brokers can affect cluster availability. Operators already on the fixed releases can skip it.","user_interaction":"no","needs_special_setup":"no","severity_if_unknown":"medium"},"cost_usd":0.000739,"input_tokens":3833,"output_tokens":712,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-111073':13A,16A '-2026':12A,15A '-714':75C '1':90C,273C '4.2.2':217C,259C '4.3.1':218C,260C '4.4.0':220C,262C 'abort':281C 'acl':211C 'affect':195C,222C 'amplif':232C 'apach':1A,215C,257C 'api':30B,73C 'authent':47B,141C,203C 'avail':197C,200C 'bound':235C,278C,315C 'broker':9A,20B,27B,67B,70C,137C,161C,177C,187C,193C 'broker-sid':69C 'buffer':111C 'case':246C 'caus':63B,180C 'check':31B 'chunk':279C 'client':7A,37B,48B,83C,142C,189C,204C 'clienttelemetryutils.decompress':95C,263C 'cluster':196C 'compress':34B,54B,79C,114C,121C,127C,151C,238C,299C 'concurr':172C 'configur':227C 'consum':160C 'crash':185C 'cve':11A,14A 'decompress':40B,93C,97C,105C,154C,247C,267C,275C,287C,311C 'default':89C,272C,317C 'degrad':183C 'enforc':264C 'equal':269C 'exampl':124C 'exceed':289C 'exhaust':8A,117C,175C 'expand':57B,131C,307C 'fulli':229C,306C 'gate':208C 'grow':108C 'gzip':126C 'gzip-compress':125C 'heap':10A,110C,138C,162C,178C,309C 'high':53B,120C,298C 'host':25B 'hundr':59B,133C 'impact':139C 'input':115C 'instead':303C 'kafka':2A,17B,19B,216C,258C 'kafka-brok':18B 'kip':74C 'kubernet':21B 'larg':158C,296C 'let':5A 'limit':45B,102C,291C 'lower':240C 'maximum':266C 'mb':91C,274C 'megabyt':61B,135C 'metric':38B,85C 'mitig':212C,254C 'multipl':192C 'outofmemoryerror':64B,182C 'output':44B,106C 'over-larg':294C 'packag':22B 'partial':253C 'payload':55B,86C,99C,122C,152C,300C 'prevent':230C 'proport':165C,249C 'push':4A 'pushtelemetri':29B,72C,146C,198C 'read':276C 'reduc':242C 'reject':302C 'repeat':170C 'request':147C,168C,173C 'resolut':255C 'self':24B 'self-host':23B 'send':50B,144C 'side':71C 'size':35B,80C,107C,159C,169C,239C,248C,268C,312C 'small':52B,119C,150C 'target':191C 'telemetri':3A 'telemetry.max.bytes':88C,234C,241C,271C 'telemetrytoolargeexcept':284C 'therefor':130C,314C 'total':288C 'upgrad':213C 'valid':76C 'version':223C 'worst':245C 'worst-cas':244C 'zero':128C","nicknames":[],"mitigations":[],"who_affected":"Any cluster running an affected Apache Kafka broker version is exposed, because PushTelemetry (KIP-714) is reachable by any authenticated client and is not gated by an ACL. Clusters where clients are fully trusted carry less practical risk, but an authenticated client that targets multiple brokers can affect cluster availability. Operators already on the fixed releases can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-28T17:17:38+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-111073","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-111073","severity":null,"published_at":"2026-10-28T17:17:38+00:00","modified_at":"2026-10-28T17:17:38+00:00","first_seen_at":"2026-10-28T17:34:08+00:00","fetched_at":"2026-10-28T17:34:08+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}