Vulnerability in Envoyproxy Envoy

CVE-2026-73550

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy copies every decoded HTTP/2 Host header value before discarding it when :authority is already present. The discarded value bypasses saveHeader, so its bytes and count are not charged against request header limits. An unauthenticated client can use HPACK indexing to submit many references to a large Host value across a bounded number of streams, forcing extreme header-copy allocation and causing the proxy to be out-of-memory killed. The relevant scope boundary is that the demonstrated amplification uses HTTP/2 HPACK and the duplicate Host discard behavior. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.006 (46.2th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 46th percentile — 46.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-73550: held from 0.006 to 0.006.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

  • Envoyproxy Envoy — versions < 1.36.10, >= 1.37.0, < 1.37.6, >= 1.38.0, < 1.38.4

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-73550?
CVE-2026-73550 is a high-severity vulnerability in Envoyproxy Envoy, classified under Missing Release of Memory after Effective Lifetime. CVSS score: 7.5/10. Published 2026-09-21.
How severe is CVE-2026-73550?
High severity. CVSS v3 base score is 7.5 out of 10.