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GHSA-2gcr-mfcq-wcc3
No affected components available
Summary
app.mount() strips the mount prefix from the incoming request path using the raw URL pathname, while route matching is performed against the percent-decoded path. This inconsistency causes the prefix to be stripped at the wrong position when the path contains percent-encoded multi-byte characters, resulting in the mounted sub-application receiving an incorrect path.
Details
When app.mount(prefix, subApp) is called, Hono calculates the number of characters to strip based on the decoded mount prefix length, but then applies that slice to the raw URL pathname. When the URL contains percent-encoded characters that expand to fewer characters when decoded (such as encoded non-ASCII characters), the two representations have different lengths, so the prefix is stripped at the wrong byte offset.
As a result, the sub-application receives a path that does not correspond to the intended sub-path — it may receive a partial or garbled path instead of the expected value after the mount prefix is removed.
This issue arises when an application uses app.mount() with paths that contain percent-encoded characters, particularly when the mount prefix itself or the request path contains encoded non-ASCII characters.
Impact
A mounted sub-application may receive an incorrectly stripped path, causing requests to be routed to unintended handlers within the sub-application.
This may lead to:
- Middleware or route handlers in the sub-application being bypassed or incorrectly matched due to the malformed path
- Requests reaching sub-application routes that the developer did not intend to be accessible via the mounted path
This issue affects applications that use app.mount() where the request URL may contain percent-encoded characters in the mount prefix or subsequent path segments.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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