cve.bz

CAPEC-79

Using Slashes in Alternate Encoding

High severityHigh likelihoodDetailed pattern

This attack targets the encoding of the Slash characters. An adversary would try to exploit common filtering problems related to the use of the slashes characters to gain access to resources on the target host. Directory-driven systems, such as file systems and databases, typically use the slash character to indicate traversal between directories or other container components. For murky historical reasons, PCs (and, as a result, Microsoft OSs) choose to use a backslash, whereas the UNIX world typically makes use of the forward slash. The schizophrenic result is that many MS-based systems are required to understand both forms of the slash. This gives the adversary many opportunities to discover and abuse a number of common filtering problems. The goal of this pattern is to discover server software that only applies filters to one version, but not the other.

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How the attack unfolds

  1. Explore

    The attacker looks for a way in.

    1. [Survey the application for user-controllable inputs] Using a browser, an automated tool or by inspecting the application, an adversary records all entry points to the application.

      4 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.
      • Manually inspect the application to find entry points.

  2. Experiment

    They probe what they found.

    1. [Probe entry points to locate vulnerabilities] The adversary uses the entry points gathered in the "Explore" phase as a target list and looks for areas where user input is used to access resources on the target host. The adversary attempts different encodings of slash characters to bypass input filters.

      2 techniques
      • Try both backslash and forward slash characters
      • Try different encodings for slash characters such as %5C

  3. Exploit

    They carry out the attack.

    1. [Traverse application directories] Once the adversary determines how to bypass filters that filter out slash characters, they will manipulate the user input to include slashes in order to traverse directories and access resources that are not intended for the user.

Prerequisites

  • The application server accepts paths to locate resources.

  • The application server does insufficient input data validation on the resource path requested by the user.

  • The access right to resources are not set properly.

Skills required

  • Low skill

    An adversary can try variation of the slashes characters.

  • Medium skill

    An adversary can use more sophisticated tool or script to scan a website and find a path filtering problem.

Signs of an attack

  • If the first path decoding process has left some invalid or denylisted characters, that may be a sign that the request is malicious.

  • Traffic filtering with IDS (or proxy) can detect request with suspicious URLs. IDS may use signature based identification to reveal such URL based attacks.

  • An adversary can use a fuzzer in order to probe for a UTF-8 encoding vulnerability. The fuzzer should generate suspicious network activity.

Consequences

What a successful attack can lead to
ImpactAffectsNote
Read DataConfidentiality
Execute Unauthorized CommandsConfidentiality, Integrity, AvailabilityRun Arbitrary Code
Gain PrivilegesConfidentiality, Access Control, Authorization

Mitigations

  • Any security checks should occur after the data has been decoded and validated as correct data format. Do not repeat decoding process, if bad character are left after decoding process, treat the data as suspicious, and fail the validation process. Refer to the RFCs to safely decode URL.

  • When client input is required from web-based forms, avoid using the "GET" method to submit data, as the method causes the form data to be appended to the URL and is easily manipulated. Instead, use the "POST method whenever possible.

  • There are tools to scan HTTP requests to the server for valid URL such as URLScan from Microsoft (http://www.microsoft.com/technet/security/tools/urlscan.mspx)

  • Be aware of the threat of alternative method of data encoding and obfuscation technique such as IP address encoding. (See related guideline section)

  • Test your path decoding process against malicious input.

  • In the case of path traversals, use the principle of least privilege when determining access rights to file systems. Do not allow users to access directories/files that they should not access.

  • Assume all input is malicious. Create an allowlist that defines all valid input to the application 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-22 Improper Limitation of a Pathname to a Restricted Directory
  • CWE-73 External Control of File Name or Path
  • CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component
  • CWE-173 Improper Handling of Alternate Encoding
  • CWE-180 Incorrect Behavior Order: Validate Before Canonicalize
  • CWE-181 Incorrect Behavior Order: Validate Before Filter
  • CWE-185 Incorrect Regular Expression
  • CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
  • CWE-697 Incorrect Comparison
  • CWE-707 Improper Neutralization

Recent CVEs with these weaknesses

  1. 4.9CVE-2026-105427

    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.

  2. 6.7CVE-2026-105426

    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.

  3. 5.5CVE-2026-123181

    A path traversal vulnerability in Ivanti Sentry before versions 10.7.4 and 10.8.3 allows a remote authenticated attacker with administrative privileges to create arbitrary directories and files with root privileges.

  4. –CVE-2026-97881

    The embedded OpenEJB HTTP server does not restrict static resource paths to the configured resource directories. A remote unauthenticated attacker can read arbitrary files accessible to the server process. Users are recommended to block ne…

  5. 9.6CVE-2026-108186

    Improper Input Validation in Zoom Workplace for Windows may allow an unauthenticated user to conduct an escalation of privilege via network access.

  6. 8.2CVE-2026-125753

    ABP Framework 2.9.0 before 10.6.2 and 10.7.0 pre-releases before 10.7.0 contain a path traversal vulnerability in DefaultBlobFilePathCalculator that allows unauthenticated attackers to access files outside the blob container. Attackers can…

  7. –CVE-2026-86811

    The stateful session bean passivation mechanism derives the on-disk file name from a client-supplied identifier without validating it. A remote attacker with access to the remote EJB service can cause session state to be read from or writt…

  8. 4.3CVE-2026-124944

    Information disclosure in the Marionette component. This vulnerability was fixed in Firefox 160.

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

Part of

Examples

Attack Example: Slashes in Alternate Encodings

Attack Example: Slashes in Alternate Encodings

The two following requests are equivalent on most Web servers:

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

is equivalent to

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

Multiple encoding conversion problems can also be leveraged as various slashes are instantiated in URL-encoded, UTF-8, or Unicode. Consider the strings

http://target server/some_directory\..%5C..%5C..\winnt

where %5C is equivalent to the \ character.

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