Weakness (CWE)
CWE-177: Improper Handling of URL Encoding (Hex Encoding)
The product does not properly handle when all or part of an input has been URL encoded.
How to prevent it (3 mitigations)
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Architecture and Design
Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
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Implementation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."
Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
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Implementation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Source: MITRE CWE-177
23 results · Feed
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High 7.5CVE-2026-118650 Public exploit
Echo: middleware.Static: `%2F`-encoded path bypasses route/group middleware guarding a statically-served path
Echo is a Go web framework. Prior to 4.16.0 and 5.4.0, a globally mounted middleware.Static instance can interpret an encoded request path differently from Echo's router because the router matches the still-encoded path while the static handler uses the decod…
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High 7.5
OpenNext Cloudflare: Cache interception can bypass middleware protection for encoded paths
OpenNext Cloudflare is an open Next.js adapter for Cloudflare. From 0.3.0 until 1.20.2, applications that enable enableCacheInterception, rely on middleware for access control, and have a matching cached protected route process encoded pathnames inconsistentl…
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Critical 9.8
Cisco Catalyst SD-WAN Manager System Account Authorization Bypass Vulnerability
A vulnerability in the API session-based authentication management of Cisco Catalyst SD-WAN Manager could allow an unauthenticated, remote attacker to access an affected system with privileges of the admin user. This vulnerability is due to improper handling …
KEV Sep 30, 2026 -
Medium 6.5
Connection redirection via percent-encoded delimiter injection in connection string hosts
PyMongo's connection string parsing decodes percent-encoded characters in the host portion before the host list is separated on its delimiters. When an application places a hostname value supplied by an unauthenticated party into a connection string, that par…
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High 7.5
fast-uri vulnerable to host confusion via percent-encoded scheme normalization
fast-uri is a URI parser for Node.js. During parsing it runs a legacy decoding pass over the scheme component and never re-escapes the result, and serialization writes the scheme back out verbatim, unlike the host component which is re-escaped. As a result an…
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Medium 6.5
Mailpit: WebSocket origin check bypass via percent-encoded path (regression of CVE-2026-22689)
Mailpit is an email testing tool and API for developers. From 1.29.0 until 1.30.6, Mailpit's server/server.go origin middleware checks the raw RequestURI for the /api/ prefix while Go's ServeMux routes using the percent-decoded URL path, and server/websockets…
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High 8.1
Velociraptor Stored XSS in URL column types
Velociraptor's web GUI allows specifying a custom type for columns in tables. The URL type takes the cell value and forms a URL which can be clicked in the GUI.The code does not limit the schemes allowed in this URL , allowing an attacker to specify a JavaScr…
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Critical 9.1
Apache Tomcat: Incorrect URL decoding in RewriteValve may allow security control bypass
Improper Handling of URL Encoding (Hex Encoding) vulnerability in Apache Tomcat's rewrite valve allowed security constraint bypass for some configurations. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.23, from 10.1.0-M1 through 10.1.56, from …
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Critical 9.1
Apache Gravitino: URL path injection via unencoded user-supplied identifiers in MCP REST client f-string URL construction, enabling path traversal to unintended API endpoints.
URL path injection via unencoded user-supplied identifiers vulnerability in Apache Gravitino. This issue affects Apache Gravitino: from 1.0.0 before 1.2.1. Users are recommended to upgrade to version 1.2.1, which fixes the issue.
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Medium 5.9
@fastify/static vulnerable to route guard bypass via encoded path separators
@fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's router treats them as literal characters. This mismatch allows attackers to bypass route-based middleware or guards that pr…
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High 7.5
Hono: Arbitrary file access via serveStatic vulnerability
Hono is a Web application framework that provides support for any JavaScript runtime. Prior to version 4.12.4, when using serveStatic together with route-based middleware protections (e.g. app.use('/admin/*', ...)), inconsistent URL decoding allowed protected…
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High 8.4
@fastify/express vulnerable to Improper Handling of URL Encoding (Hex Encoding)
The @fastify/express plugin adds full Express compatibility to Fastify. A security vulnerability exists in @fastify/express prior to version 4.0.3 where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., `/%6…
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High 8.4
Fastify Middie Middleware Path Bypass
@fastify/middie is the plugin that adds middleware support on steroids to Fastify. A security vulnerability exists in @fastify/middie prior to version 9.1.0 where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (…
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High 7.5
Apache Linkis: Arbitrary File Read via Double URL Encoding Bypass
A vulnerability in Apache Linkis. Problem Description When using the JDBC engine and da When using the JDBC engine and data source functionality, if the URL parameter configured on the frontend has undergone multiple rounds of URL encoding, it may bypass the …
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Low 3.1
Improper Handling of URL Encoding (Hex Encoding) in GitLab
GitLab has remediated an issue in GitLab EE affecting all versions from 18.4 before 18.4.4, and 18.5 before 18.5.2 that could have allowed an authenticated user to gain CSRF tokens by exploiting improper input validation in repository references combined with…
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Low 2.3
QTS, QuTS hero
An improper handling of URL encoding (Hex Encoding) vulnerability has been reported to affect several QNAP operating system versions. If exploited, the vulnerability could allow remote attackers to run the system into unexpected state. We have already fixed t…
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Medium 5.8
Access rules for PingAccess may be circumvented with URL-encoded characters
Improper handling of canonical URL-encoding may lead to bypass not properly constrained by request rules.
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Medium 4.8
Incorrect processing of fragment in the URL leads to Authorization Bypass in Traefik
Traefik is an open source HTTP reverse proxy and load balancer. When a request is sent to Traefik with a URL fragment, Traefik automatically URL encodes and forwards the fragment to the backend server. This violates RFC 7230 because in the origin-form the URL…
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Medium 6.5
A flaw was found in Ceph, relating to the URL processing on RGW backends. An attacker can exploit the URL processing by…
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Critical 9.1CVE-2022-3782 Public exploit
Keycloak vulnerable to path traversal via double URL encoding
keycloak: path traversal via double URL encoding. A flaw was found in Keycloak, where it does not properly validate URLs included in a redirect. An attacker can use this flaw to construct a malicious request to bypass validation and access other URLs and pote…
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Medium 5.3
The curl URL parser wrongly accepts percent-encoded URL separators like '/'when decoding the host name part of a URL, m…
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High —
Path Traversal in superstatic
Affected of `superstatic` are vulnerable to path traversal when used on Windows. Additionally, it is vulnerable to path traversal on other platforms combined with certain Node.js versions which erroneously normalize `\\` to `/` in paths on all platforms (a kn…
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Medium 5.3
vercel/serve allows access to restricted files if filename is URL encoded.
serve node module suffers from Improper Handling of URL Encoding by permitting access to ignored files if a filename is URL encoded.