Pomerium: Pre-Auth Memory Exhaustion via Unbounded zstd Decompression in HPKE Callback

Summary

Pomerium is an identity and context-aware access proxy. Prior to 0.32.8, decodeQueryStringV2 in pkg/hpke/url.go performs zstd decompression of attacker-controlled data without an output-memory limit when DecryptURLValues processes HPKE V2 values for Stateless.Callback in internal/authenticateflow/stateless.go. In hosted or stateless authentication deployments, an unauthenticated attacker can obtain the receiver key from /.well-known/pomerium/hpke-public-key, provide a matching attacker-controlled sender key, and send a compressed payload to /.pomerium/callback that expands before validateSenderPublicKey rejects the sender. This can allocate hundreds of megabytes per request, exhaust proxy memory, crash or degrade the process, and block access to applications protected by the deployment. Stateful deployments are not affected because the stateful callback verifies its HMAC signature before decryption and decompression. This issue is fixed in version 0.32.8.

Timeline

1. Sep 17, 2026, 7:49 PM UTCCVE published
2. Sep 17, 2026, 8:19 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: yes · Technical impact: partial

3. Sep 17, 2026, 8:19 PM UTCRecord last updated

Affected versions

• pomerium pomerium

  fixed in 0.32.8

• github.com/pomerium/pomeriumGo

  From 0.32.6 · fixed in 0.32.8

References 3