CVE-2026-73550
The discarded value bypasses saveHeader, so its bytes and count are not charged against request header limits.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.55%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.55% probability · 46th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-401
- Affected
- envoyproxy/envoy
- Source
- security-advisories@github.com
EPSS moved from 0.9% on 22 September 2026 to 0.6% on 26 October 2026.
References
- https://github.com/envoyproxy/envoy/commit/0910997f70e91d2d20c329bb507bfce44ce01f80Patch
- https://github.com/envoyproxy/envoy/commit/1fec994c868df008cdd4ae285aab58a196fd31f2Patch
- https://github.com/envoyproxy/envoy/commit/3fd0ffee7ac87adf3bc6e421656bb96310512300Patch
- https://github.com/envoyproxy/envoy/commit/fc75d8e35b0d11acbae18b63a0bd96e32e84f61bPatch
- https://github.com/envoyproxy/envoy/releases/tag/v1.36.10Release Notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.37.6Release Notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.38.4Release Notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.39.1Release Notes
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-qgf6-qvhw-4hvhExploit, Vendor Advisory
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-qgf6-qvhw-4hvhExploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.