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The `decode-uri-component` package is a widely used Node.js library for decoding URI components, such as query strings and path segments. Its core function, decodeUriComponent(), is often called indirectly by popular frameworks and dependencies that process URL or query data. The vulnerability, identified as CVE-2026-45822, resides in the algorithmic implementation of this decoding process. The issue is triggered when the `decode()` function processes a string that contains a large number of `%` (percent) characters. For every `%` found in the input, the function generates a new token and subsequently invokes the `decodeComponents()` helper.
The critical flaw is that this parsing and decoding operation exhibits super-linear, or exponential, time complexity relative to the number of `%` tokens present. For a typical, non-malicious input, this overhead is negligible. However, an attacker can craft a specific payload composed almost entirely of `%` characters (e.g., a long string of `%ab` tokens) to exploit this algorithmic inefficiency. The performance degradation is severe and demonstrable: processing 200 such tokens takes approximately 0.7 seconds, 700 tokens take roughly 6 seconds, and a payload of 1,400 tokens can consume about 33 seconds of CPU time.
This behavior represents a classic algorithmic complexity attack. The library’s parsing routine does not scale linearly, causing the Node.js event loop to be blocked for an extended period as it struggles to process the malicious input. The primary impact of this vulnerability is a Denial of Service (DoS). By repeatedly sending requests containing these oversized, malformed inputs, an attacker can exhaust server-side CPU resources, leading to application unresponsiveness and making the service unavailable to legitimate users. Crucially, this is a resource consumption issue and does not lead to memory corruption, data breaches, or remote code execution. The vulnerability affects all versions of the package from `0.1.0` up to, but not including, 0.5.0. The official patch was released in version 0.5.0.
DailyCVE Form:
Platform: Node.js / Linux/macOS/Windows
Version: 0.1.0 – 0.4.1
Vulnerability: Denial of Service (Algorithmic Complexity)
Severity: Moderate (CVSS 6.6)
date: June 30, 2026
Prediction: Patch available (v0.5.0)
What Undercode Say:
Analytics:
The vulnerability is triggered by the `decode()` function’s super-linear parsing time when processing strings with a high density of `%` characters. The performance impact is clear: 200 `%ab` tokens ≈ 0.7s, 700 tokens ≈ 6s, and 1400 tokens ≈ 33s. The CVSS score is 6.6 (Medium), with an EPSS score of 0.30%, indicating a low probability of exploitation in the next 30 days. The vulnerability is fixed in version 0.5.0.
Exploit: (Educational Purposes!)
An attacker can exploit this by sending a crafted payload to any application that decodes user-supplied input using the vulnerable library. A proof-of-concept is a long string of `%ab` tokens:
Example of a malicious payload (truncated for brevity) PAYLOAD="%ab%ab%ab%ab%ab%ab%ab%ab%ab%ab..." Repeated thousands of times
Sending this payload in a query parameter (?data= + $PAYLOAD) to a vulnerable endpoint will cause excessive CPU usage.
Protection:
Upgrade to `[email protected]` immediately. If an immediate upgrade is not possible, implement a workaround by strictly limiting the size of the input string passed to decodeUriComponent().
Impact:
Successful exploitation leads to a Denial of Service (DoS) condition. An attacker can cause significant CPU consumption and event-loop blocking, rendering the application unresponsive to legitimate user requests. There is no impact on confidentiality or integrity.
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Sources:
Reported By: github.com
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