CAPEC-71

Using Unicode Encoding to Bypass Validation Logic

High severityMedium likelihoodDetailed pattern

An attacker may provide a Unicode string to a system component that is not Unicode aware and use that to circumvent the filter or cause the classifying mechanism to fail to properly understanding the request. That may allow the attacker to slip malicious data past the content filter and/or possibly cause the application to route the request incorrectly.

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Ask an AI about this attack pattern
How the attack unfolds
Prerequisites
Skills required
Signs of an attack
Consequences
Mitigations
Weaknesses it exploits
Related attack patterns
Examples

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Explain the attack pattern CAPEC-71: Using Unicode Encoding to Bypass Validation Logic: how it unfolds, what it needs and how to prevent and detect it in my systems. Use https://capec.mitre.org/data/definitions/71.html and https://cve.bz/cve/capec/71?via=ask-ai-copy, which lists recent CVEs with the weaknesses it exploits. Cite the sources.

Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this attack pattern's id and public links.

How the attack unfolds

Explore
The attacker looks for a way in.
1. [Survey the application for user-controllable inputs] Using a browser or an automated tool, an attacker follows all public links and actions on a web site. They record all the links, the forms, the resources accessed and all other potential entry-points for the web application.
  3 techniques
  - Use a spidering tool to follow and record all links and analyze the web pages to find entry points. Make special note of any links that include parameters in the URL.
  - Use a proxy tool to record all user input entry points visited during a manual traversal of the web application.
  - Use a browser to manually explore the website and analyze how it is constructed. Many browsers' plugins are available to facilitate the analysis or automate the discovery.
Experiment
They probe what they found.
1. [Probe entry points to locate vulnerabilities] The attacker uses the entry points gathered in the "Explore" phase as a target list and injects various Unicode encoded payloads to determine if an entry point actually represents a vulnerability with insufficient validation logic and to characterize the extent to which the vulnerability can be exploited.
  3 techniques
  - Try to use Unicode encoding of content in Scripts in order to bypass validation routines.
  - Try to use Unicode encoding of content in HTML in order to bypass validation routines.
  - Try to use Unicode encoding of content in CSS in order to bypass validation routines.

Prerequisites

Filtering is performed on data that has not be properly canonicalized.

Skills required

Medium skill
An attacker needs to understand Unicode encodings and have an idea (or be able to find out) what system components may not be Unicode aware.

Signs of an attack

Unicode encoded data is passed to APIs where it is not expected

Consequences

What a successful attack can lead to
Impact	Affects	Note
Bypass Protection Mechanism	Confidentiality, Access Control, Authorization
Execute Unauthorized Commands	Confidentiality, Integrity, Availability	Run Arbitrary Code
Modify Data	Integrity
Unreliable Execution	Availability

Mitigations

Ensure that the system is Unicode aware and can properly process Unicode data. Do not make an assumption that data will be in ASCII.
Ensure that filtering or input validation is applied to canonical data.
Assume all input is malicious. Create an allowlist that defines all valid input to the software system based on the requirements specifications. Input that does not match against the allowlist should not be permitted to enter into the system.

Weaknesses it exploits

CWE-20 Improper Input Validation
CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component
CWE-172 Improper Encoding or Decoding of Data
CWE-173 Improper Handling of Alternate Encoding
CWE-176 Improper Handling of Unicode Encoding
CWE-179 Incorrect Behavior Order: Early Validation
CWE-180 Incorrect Behavior Order: Validate Before Canonicalize
CWE-183 Permissive List of Allowed Inputs
CWE-184 Incomplete List of Disallowed Inputs
CWE-692 Incomplete Denylist to Cross-Site Scripting
CWE-697 Incorrect Comparison

Recent CVEs with these weaknesses

9.6CVE-2026-1081862026-11-10
Improper Input Validation in Zoom Workplace for Windows may allow an unauthenticated user to conduct an escalation of privilege via network access.
4.9CVE-2026-1054272026-11-10
Improper input validation in Ivanti EPMM before version 12.10.0.1, 12.9.0.3, and 12.8.0.5 allows a remote authenticated attacker with admin privileges to permanently disable all Apache HTTPS services resulting in denial of service.
6.7CVE-2026-1054262026-11-10
Improper input validation in Ivanti EPMM before version 12.10.0.1, 12.9.0.3, and 12.8.0.5 allows a remote authenticated attacker with admin privileges to set arbitrary Linux kernel parameters as root.
4.3CVE-2026-1231782026-11-10
An insufficient input validation vulnerability in the listed NETGEAR Orbi Models router allows an authenticated administrator connected to the local network to execute unauthorized commands and modify the router’s software and functionalit…
7.0CVE-2026-164782026-11-10
Permissive list of allowed inputs vulnerability in TÜBİTAK BİLGEM Software Technologies Research Institute pardus-nvidia-installer allows Privilege Escalation. This issue affects pardus-nvidia-installer: before 2.0.1.
6.3CVE-2026-1258712026-11-10
The sourcecache expansion module in MISP Modules (misp-modules) contains a Server-Side Request Forgery (SSRF) vulnerability. When a user with permission to create or modify attributes of type 'link' or 'url' submits an attribute value, the…
5.5CVE-2026-1257032026-11-10
A flaw was found in the GStreamer gst-plugins-bad MXF plugin. Insufficient bounds checks when parsing crafted VANC data can cause an out-of-bounds read in the demuxer, while an incorrect buffer size calculation when muxing multiple ancilla…
7.7CVE-2026-1253682026-11-10
OmniAgent through commit 12b98c5 contains an approval bypass vulnerability in ReflexionAgent._is_safe_bash_command that treats any command starting with find as safe without inspecting -execdir arguments. Prompt-injected agents can run fin…

The newest records naming one of them. Each weakness's page lists them all.

Part of: CAPEC-267 Leverage Alternate Encoding

Examples

A very common technique for a Unicode attack involves traversing directories looking for interesting files. A…

A very common technique for a Unicode attack involves traversing directories looking for interesting files. An example of this idea applied to the Web is

http://target.server/some_directory/../../../winnt

In this case, the attacker is attempting to traverse to a directory that is not supposed to be part of standard Web services. The trick is fairly obvious, so many Web servers and scripts prevent it. However, using alternate encoding tricks, an attacker may be able to get around badly implemented request filters.

In October 2000, an adversary publicly revealed that Microsoft's IIS server suffered from a variation of this problem. In the case of IIS, all the attacker had to do was provide alternate encodings for the dots and/or slashes found in a classic attack. The Unicode translations are

. yields C0 AE
/ yields C0 AF
\ yields C1 9C

Using this conversion, the previously displayed URL can be encoded as

http://target.server/some_directory/%C0AE/%C0AE/%C0AE%C0AE/%C0AE%C0AE/winnt