What is CVE-2026-73550?

CVE-2026-73550 is Envoy: HTTP/2 Discarded Host Header 200 GB Header-Copy OOM in Envoy. The supplied enrichment data classifies it as Unclassified mapped to CWE-401 CWE-401.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-73550. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-73550 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

A public PoC is not confirmed from current sources for CVE-2026-73550. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-73550 using CVSS 7.5, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

high

CVE-2026-73550

CVE-2026-73550 — Envoy: HTTP/2 Discarded Host Header 200 GB Header-Copy OOM in Envoy

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 Sep 21, 2026Updated Sep 21, 2026Sources: NVD, envoyproxy (CNA), GitHub, Red Hat (VEX), SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Unreported

no source claims exploitation

EPSS

ahead of 0% of scored CVEs

Affects

envoyproxy

4 products listed

CVSS base

7.5

high

Remediation

The vendor's own words where we have them.

Upgrade envoy to a fixed release. Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

Red Hat VEX · CVE-2026-73550

fixed20affected0not affected105

vendor_fix: See Red Hat OpenShift Service Mesh 3.0.15 documentation at https://docs.redhat.com/en/documentation/red_hat_openshift_service_mesh/3.0

vendor_fix: See Red Hat OpenShift Service Mesh 3.1.12 documentation at https://docs.redhat.com/en/documentation/red_hat_openshift_service_mesh/3.1

vendor_fix: See Red Hat OpenShift Service Mesh 3.2.9 documentation at https://docs.redhat.com/en/documentation/red_hat_openshift_service_mesh/3.2

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
envoyproxy	envoy	< 1.36.10	Vulnerable
envoyproxy	envoy	>= 1.37.0, < 1.37.6	Vulnerable
envoyproxy	envoy	>= 1.38.0, < 1.38.4	Vulnerable
envoyproxy	envoy	>= 1.39.0, < 1.39.1	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Availability

High

Confidentiality

None

Integrity

None

Scope

Unchanged

Attack Complexity

Low

Attack Vector

Network

Privileges Req

None

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
7.5	CVSS 3.1	high	3.9	3.6	GitHub (CNA), envoyproxy (CNA), Red Hat (VEX)

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-401 · Missing Release of Memory after Effective Lifetime

DoS: Crash, Exit, or Restart
DoS: Instability
DoS: Resource Consumption (CPU)
DoS: Resource Consumption (Memory)

Mitigation: Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone. For example, glibc in Linux provides protection against free of invalid pointers. When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391]. To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

Weakness & attack patterns

CWE-401

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Search application, proxy, and WAF logs for requests touching /2.
Prioritize edge telemetry for network-reachable envoy.

web/proxy/WAF logsapplication logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 7.5 (AV:N)
Sep 21, 2026 · NVD
Initial · CVE published
Sep 21, 2026 · NVD
CVE published by MITRE.
Sep 21, 2026 · SOCRadar CTI

References

18 on the record

github.com/envoyproxy/envoy/commit/0910997f70e91d2d20c329bb507bfce44ce01f80
Exploit, Third Party Advisory, Mitre
github.com/envoyproxy/envoy/commit/1fec994c868df008cdd4ae285aab58a196fd31f2
Exploit, Third Party Advisory, Mitre
github.com/envoyproxy/envoy/commit/3fd0ffee7ac87adf3bc6e421656bb96310512300
Exploit, Third Party Advisory, Mitre
github.com/envoyproxy/envoy/commit/fc75d8e35b0d11acbae18b63a0bd96e32e84f61b
Exploit, Third Party Advisory, Mitre
github.com/envoyproxy/envoy/releases/tag/v1.36.10
Exploit, Third Party Advisory, Mitre
github.com/envoyproxy/envoy/releases/tag/v1.37.6
Exploit, Third Party Advisory, Mitre
github.com/envoyproxy/envoy/releases/tag/v1.38.4
Exploit, Third Party Advisory, Mitre
github.com/envoyproxy/envoy/releases/tag/v1.39.1
Exploit, Third Party Advisory, Mitre

Elsewhere on this site

envoyproxyevery CVE for this vendor
Unclassifiedsame class
CWE-401other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-73550 is Envoy: HTTP/2 Discarded Host Header 200 GB Header-Copy OOM in Envoy, a high vulnerability affecting envoy from envoyproxy. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-73550. Public exploit evidence is: A public PoC is not confirmed from current sources for CVE-2026-73550. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 7.5 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.