VulnerabilityPublished 23 Oct 2026Updated 28 Oct 2026

CVE-2026-118264: Rejected WebSocket upgrades can bypass Echo route-level access controls

Affects github.com/labstack/echo/v4Source GCVE Database

Authoritative record:CVE-2026-118264· Critical 9.1

Not known to be exploited · CVSS 9.1 Critical : upgrade to 4.16.1 as a priority.

Data as of 28 Oct 2026, 20:14 UTC

CVSS 4.0 base score

9.1Critical

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

Patch: Available – fixed in 4.16.1, 5.4.1

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: High
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 Oct 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 github.com/labstack/echo/v4 to 4.16.1; github.com/labstack/echo/v5 to 5.4.1.

Affected software

Product	Affected	Fixed in
Gogithub.com/labstack/echo/v4	Affected >=4.0.0 <4.16.1	Fixed in 4.16.1
Gogithub.com/labstack/echo/v5	Affected >=5.0.0 <5.4.1	Fixed in 5.4.1

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

AI-suggested

Upgrade Echo to version v4.16.1 or later, or v5.4.1 or later, where the vulnerability is fixed. The fix ensures that WebSocket upgrades are properly validated by the upstream before entering a tunnel. As a workaround, reject WebSocket upgrade requests before they reach affected Echo proxy routes or enforce authorization independently at every upstream resource. Note that simply returning a non-101 response from the upstream does not mitigate the vulnerability.

Description

Echo versions prior to v4.16.1 and v5.4.1 contain a vulnerability where rejected WebSocket upgrade requests can bypass route-level access controls. This occurs because Echo's proxy middleware forwards subsequent HTTP requests on a connection with a rejected upgrade directly to the upstream without passing through Echo's router or middleware, potentially bypassing authentication or authorization enforced at Echo routes. Exploitation requires an accessible proxy route, an upstream that rejects the upgrade without closing the connection, and a target resource on that upstream without its own authorization. Fixed in versions v4.16.1 and v5.4.1.

Impact

This vulnerability allows an attacker to bypass Echo's route-level authentication or authorization controls by exploiting how rejected WebSocket upgrade requests are handled. The attacker can send HTTP requests that are forwarded directly to the upstream server without passing through Echo's access controls, potentially accessing protected resources if the upstream does not enforce its own authorization. However, the vulnerability does not allow arbitrary host proxying or bypass upstream authentication mechanisms. The CVSS 4.0 score is 9.1 (critical), reflecting the high impact of unauthorized access.

Summary

The Echo web framework's proxy middleware improperly handles WebSocket upgrade requests by selecting a raw tunnel before validating if the upstream accepts the upgrade. If the upstream rejects the upgrade but keeps the connection alive with an ordinary HTTP response, subsequent HTTP requests on that connection bypass Echo's routing and route-specific middleware, potentially circumventing authentication or authorization controls enforced at Echo routes. This vulnerability affects Echo versions from v4.0.0 up to but not including v4.16.1 and from v5.0.0 up to but not including v5.4.1. The issue is fixed by routing WebSocket upgrades through Go's HTTP reverse proxy and only entering a tunnel after a valid upstream upgrade response. Workarounds include rejecting WebSocket upgrade requests before they reach vulnerable proxy routes or enforcing authorization independently at upstream resources.

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') (opens in a new tab)
Base weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
Implementation
Use a web server that employs a strict HTTP parsing procedure, such as Apache.
Implementation
Use only SSL communication.
Implementation
Terminate the client session after each request.
OWASP Cheat Sheets
REST Assessment (opens in a new tab)
REST Security (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V13.2.5 (opens in a new tab)
Attack patterns
HTTP Response Smuggling (opens in a new tab)
HTTP Request Smuggling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-863Incorrect Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #17OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 28 Oct 2026, 20:14 UTC

WeaknessesCWE-444, CWE-863

Technical details

References

Community reviews

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