CVE-2026-47774

Summary

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1, a vulnerability in Envoy's HTTP/2 downstream request processing allows an unauthenticated remote client to trigger excessive memory consumption, potentially resulting in OOM termination of the Envoy process and denial of service. The issue arises from the combination of two behaviors. First, cookie header bytes are not fully accounted for during request header size validation in Envoy. Second, HPACK header block limits in oghttp2/quiche are enforced on encoded bytes without a corresponding limit on total decoded header size. Together, these behaviors allow a malicious client to cause large decoded header allocations while bypassing the intended request header size protections. Versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1 contain a fix. No complete workaround is known short of applying a fix. Possible temporary mitigations include disabling downstream HTTP/2 where operationally feasible; enforcing stricter request header and cookie limits before traffic reaches Envoy; and monitoring Envoy memory usage for abnormal growth under HTTP/2 traffic.

Affected Software

VendorProductVersion RangeStatus
envoyproxyenvoy< 1.35.11affected
envoyproxyenvoy>= 1.36.0, < 1.36.7affected
envoyproxyenvoy>= 1.37.0, < 1.37.3affected
envoyproxyenvoy>= 1.38.0, < 1.38.1affected

Weaknesses

  • CWE-405: CWE-405: Asymmetric Resource Consumption (Amplification)
  • CWE-770: CWE-770: Allocation of Resources Without Limits or Throttling

ADP Enrichment

CVE Program Container

Additional References

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: yes
    • Technical Impact: partial

envoy: envoy: HTTP/2 Remote Denial of Service via HPACK compression bomb and Slowloris-style attack

Additional References

References