Releases

v1.21.1 is a security-focused patch release addressing findings from a formal security audit, including XSS, gzip bomb, and memory amplification vulnerabilities — upgrade immediately.

• securityUpgrade immediately — multiple audit findings patched

  This release backports fixes from a formal security audit (V01–V07). The vulnerabilities include a stored XSS on status pages, a gzip bomb in the OTLP ingestion path, memory amplification via malformed native histogram payloads, and gossip port exposure to flood/OOM attacks. These are not theoretical — they are exploitable by any client that can reach your Cortex endpoints. Upgrade to v1.21.1 now. After upgrading, review your -distributor.otlp-max-recv-msg-size setting; the default may be too permissive depending on your ingest volume.

• securityAudit your /config endpoint exposure

  Prior to this release, Swift, etcd, Redis, and HTTP basic-auth credentials were exposed in plaintext on the /config endpoint. If that endpoint was accessible to internal users or scraping systems, treat those credentials as compromised and rotate them. Going forward, restrict /config access via network policy or auth middleware regardless of masking.

• enhancementHarden memberlist gossip with new bounding flags

  Three new flags (-memberlist.packet-read-timeout, -memberlist.max-packet-size, -memberlist.max-concurrent-connections) cap inbound gossip TCP behavior. The defaults are reasonable, but if your Cortex cluster is exposed to less-trusted network segments or you've seen gossip-related OOM events, tune these explicitly. Add them to your Helm values or config management before the next planned maintenance window.

Cortex v1.21.0 graduates several experimental features to stable, fixes multiple PRW2 data corruption and panic bugs, and introduces a new Parquet mode for Store Gateway alongside an Overrides API.

• breakingAudit and update renamed flags before upgrading

  Several flags were renamed: -experimental.ruler.enable-api → -ruler.enable-api, -experimental.alertmanager.enable-api → -alertmanager.enable-api, -distributor.otlp.enable-type-and-unit-labels is now a no-op (consolidated into -distributor.enable-type-and-unit-labels), and parquet cache flags/configs dropped 'queryable' from their names. The users-scanner cleanup-interval became update-interval. Old flags are deprecated but not removed yet — audit your config files and Helm values now, before they disappear in a future release.

• breakingPRW2 data corruption and panic fixes require validation of existing pipelines

  Three separate bugs in the Remote Write V2 handler were fixed: shallow copying of Samples/Histograms caused data corruption, dirty sync.Pool reuse caused index-out-of-range panics, and Symbols backing array wasn't cleared on pool return causing memory leaks. If you're using PRW2, treat this upgrade as mandatory. Validate your ingestion pipeline after upgrading and check that downstream metrics are intact.

• enhancementBucket index is now on by default — verify storage permissions

  The bucket index is enabled by default in this release. If your object storage IAM policies restrict list operations or your Cortex deployment had bucket index disabled intentionally, verify that the bucket index can be written and read correctly post-upgrade. Cortex will generate and maintain the index automatically, but storage permission errors will surface as query failures rather than obvious configuration errors.