VulnerabilityPublished 21 Sep 2026Updated 28 Sep 2026

CVE-2026-73550: envoyproxy envoy · Memory Leak

Affects envoyproxy envoySource CVE Database V5

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Not known to be exploited · CVSS 7.5 High · fixed in 1.39.1 : patch envoyproxy envoy soon.

Data as of 5 Nov 2026, 00:01 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.5% chance of exploitation in 30 days – higher than 46% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.39.1, 1.38.4, 1.37.6 +1

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade envoy and envoyproxy/envoy to 1.39.1, 1.38.4, 1.37.6 or 1.36.10.

Affected software

Product	Affected	Fixed in
envoyproxyenvoy	Affected >=1.39.0 <1.39.1	Fixed in 1.39.1
envoyproxyenvoy	Affected >=1.38.0 <1.38.4	Fixed in 1.38.4
envoyproxyenvoy	Affected >=1.37.0 <1.37.6	Fixed in 1.37.6
envoyproxyenvoy	Affected <1.36.10	Fixed in 1.36.10
GitHubenvoyproxy/envoy`pkg:github/envoyproxy/envoy`Other threats	Affected <1.36.10 >=1.37.0 <1.37.6 >=1.38.0 <1.38.4 >=1.39.0 <1.39.1	Fixed in 1.36.10 1.37.6 1.38.4 1.39.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

This vulnerability is fixed in Envoy versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1. Users should upgrade to one of these versions or later to remediate the issue. No other mitigation is indicated by the vendor advisory.

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.

Impact

An unauthenticated attacker can exploit this vulnerability to cause a denial-of-service condition by forcing Envoy to allocate excessive memory, leading to the proxy being killed due to out-of-memory. There is no impact on confidentiality or integrity reported.

Summary

Envoy proxy, before versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1, improperly manages memory when processing HTTP/2 Host headers. Specifically, when the :authority header is already present, Envoy copies and then discards additional Host header values without charging them against request header limits. An attacker can exploit this by using HPACK indexing to submit many references to a large Host value across multiple streams, causing excessive header-copy allocations. This leads to memory exhaustion and potential out-of-memory termination of the proxy process. The vulnerability is identified as CWE-401 (Missing Release of Memory after Effective Lifetime) and has a CVSS 3.1 score of 7.5 (high severity).

CWE-401Missing Release of Memory after Effective Lifetime (opens in a new tab)
Variant weaknessLikelihood of exploit: Medium
The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.
Implementation · Libraries or Frameworks
Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
Architecture and Design
Use an abstraction library to abstract away risky APIs. Not a complete solution.
Architecture and Design · Build and Compilation
Consider using the Boehm-Demers-Weiser garbage collector (bdwgc), which can help avoid leaks.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 29 Sep 2026, 02:04 UTC

WeaknessesCWE-401

Technical details

References

Community reviews

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