CVE-2026-84363
ADVISORY - githubSummary
Summary
Hono's query parsing does not stop at the URL fragment: a ? appearing after a # is treated as the start of a query string. As a result, the application can read request parameters that no other component involved in handling the request can see.
Details
A fragment is never part of the query, and every standard URL consumer — browsers, new URL(), reverse proxies — ignores everything from the first # onward. Hono's routing followed that rule; its query helpers did not.
For one and the same request, this produces an interpretation differential:
- A component in front of the application that inspects the query string — filtering rules, parameter allow/deny lists, access logging — observes no parameters, while the application reads and acts on them.
- The cache middleware removed the fragment when building its cache key, so a response influenced by parameters carried inside the fragment could be stored under a key that did not reflect them and later returned to other users.
The same divergence reaches request validation and any middleware that reads query parameters.
This requires a request target containing a literal # to reach the application. Deployments on runtimes that normalise such a target — including Cloudflare Workers — are not affected, and neither are those behind an intermediary that strips the fragment.
Impact
An attacker can cause the application to act on parameters that components in front of it never observe.
This may lead to:
- filtering rules, allow/deny lists, and audit logging being blind to parameters the application still processes
- a cached response being stored under a key that does not reflect the parameters used to produce it, and served to other users
- stored cross-site scripting, where such a parameter is reflected into a cached HTML response without escaping
This issue affects applications that read query parameters and run on a runtime that passes a literal # through to the request URL.
Common Weakness Enumeration (CWE)
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
GitHub
2.2
CVSS SCORE
5.9medium| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| hono | npm | - | - | <4.13.5 | 4.13.5 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
A successful attack depends on conditions beyond the attacker's control, requiring investing a measurable amount of effort in research, preparation, or execution against the vulnerable component before a successful attack.
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.
The vulnerable system can be exploited without interaction from any user.
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.
There is no loss of confidentiality.
There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any or all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
There is no impact to availability within the impacted component.
NIST
2.2