CVE Intelligence
High exploit reference

CVE-2026-47774 — Envoy vulnerable to HTTP/2 memory exhaustion via cookie header size bypass and HPACK amplification

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.

Published Jun 17, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 1.1% (30-day exploitation probability)+10
  • Technical severity (high)+6
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

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

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
1.05%
ahead of 64% of scored CVEs · Oct 14, 2026
Affects
Envoyproxy
Envoy and 1 more
CVSS base
7.5
High · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented mitigation — github.com (NIST National Vulnerability Database)
  • Documented mitigation — www.openwall.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Envoyproxy Envoy, Red Hat Openshift Service Mesh).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the documented mitigations until a definitive fix is available.
  4. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Envoyproxy Envoy < 1.35.11≥ 1.36.0 and < 1.36.7≥ 1.37.0 and < 1.37.3version 1.38.0 Vulnerable NIST National Vulnerability Database
Envoyproxy Envoy version < 1.35.11version >= 1.36.0, < 1.36.7version >= 1.37.0, < 1.37.3version >= 1.38.0, < 1.38.1 Vulnerable CVE Program (cve.org) e CISA ADP
Red Hat Openshift Service Mesh ≥ 2.6 and < 2.6.17≥ 3.0 and < 3.0.12≥ 3.1 and < 3.1.9≥ 3.2 and < 3.2.6≥ 3.3 and < 3.3.4 Vulnerable NIST National Vulnerability Database

Attack characteristics

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

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

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

ScoreVersionSeverityExpl.ImpactScored by
7.5 CVSS 3.1 High 3.9 3.6 security-advisories@github.com via NIST National Vulnerability Database
7.5 CVSS 3.1 High 3.9 3.6 0b0ca135-0b70-47e7-9f44-1890c2a1c46c via NIST National Vulnerability Database
7.5 CVSS 3.1 High — — GitHub_M via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: security-advisories@github.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-405

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 1.05%

Detection

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

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · envoyproxy/envoy
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 7.5
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVE published
    Jun 17, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

10 on the record

Elsewhere on this site

Envoyproxy
every CVE for this vendor
CWE-405
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-73547 Envoy ext_authz: request `:path` pseudoheader dereferenced w/o null check 24d
  • CVE-2026-48090 Envoy HTTP: OAuth2 filter late async token completion after stream teardown (UAF / crash risk) Jun 26, 2026
  • CVE-2026-47220 Envoy: Segmentation fault when using %REQUESTED_SERVER_NAME% in log format Jun 26, 2026
  • CVE-2026-47205 Envoy: ext_authz Use-After-Free during Stream Teardown with Per-Route Overrides Jun 26, 2026
  • CVE-2026-48706 Envoy Heap Buffer Overflow in TcpStatsdSink Jun 26, 2026
  • CVE-2026-48743 Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length Jun 26, 2026

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 record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-47774 is "Envoy vulnerable to HTTP/2 memory exhaustion via cookie header size bypass and HPACK amplification", rated High. It affects Envoy (Envoyproxy); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 1.05% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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