Weakness (CWE)
CWE-174: Double Decoding of the Same Data
The product decodes the same input twice.
How to prevent it (4 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
Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.
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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-174
8 results · Feed
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Low 3.7
mongorestore may restore encoded collection names into an unintended collection
MongoDB Database Tools mongorestore incorrectly URL-decodes an original collection name read from metadata when the corresponding dump filename has been truncated. A database user who can create and populate a suitably encoded collection can cause a later aut…
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Medium 5.3
@hono/node-server: `serveStatic` decodes the request path a second time, leading to bypass of middleware on static paths
@hono/node-server allows running the Hono application on Node.js. From 1.19.10 until 2.1.3, serveStatic decodes a request path a second time after Hono has already decoded it for routing, so a malformed percent-encoded sequence can make route middleware evalu…
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Medium 5.9
Echo: Static Middleware Double-Unescape Path Traversal
Echo is a Go web framework. Prior to 4.15.3 and 5.2.0, middleware.Static can decode an already decoded Request.URL.Path a second time. Double-encoded separators can consequently be reconstructed before filesystem resolution. This can reach a file under a guar…
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Medium 5.3
Hono: `serveStatic` decodes the request path a second time, leading to bypass of middleware on static paths
Hono is a Web application framework that provides support for any JavaScript runtime. From 4.12.4 until 4.13.11, serveStatic can interpret a malformed percent-encoded path differently from upstream routing middleware and bypass protection for a static prefix.…
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Medium 5.3
Hono 4.12.4 before 4.13.11 Middleware Bypass via serveStatic Double Decoding
Hono from 4.12.4 before 4.13.11 contains a middleware bypass vulnerability in serveStatic that allows unauthenticated attackers to skip prefix middleware by exploiting double path decoding. Attackers can send malformed percent-encoded paths that the router ma…
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Critical 9.4CVE-2026-93903 Public exploit
LiteSpeed Web Server (LSWS) before 6.3.7 build 1 mishandles internal redirect URL validation in a certain "corner case"…
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Medium 4.3
Canva Desktop before v1.125.0 performed double decoding in the deeplink handler. A threat actor could cause the applica…
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High 7.5
fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding
fast-uri is a URI parser for Node.js. It decodes percent escapes in a hostname during parsing and then decodes the parsed hostname a second time during authority recomposition, so a single call to normalize or resolve can turn nested percent-encoded input int…