{"id":867,"date":"2026-05-14T07:50:47","date_gmt":"2026-05-14T07:50:47","guid":{"rendered":"https:\/\/www.kacateknologi.com\/en\/?p=867"},"modified":"2026-05-14T09:21:12","modified_gmt":"2026-05-14T09:21:12","slug":"1750-content-spoofing-vulnerability-using-a-naughty-string-that-affected-audit-trail-integrity","status":"publish","type":"post","link":"https:\/\/www.kacateknologi.com\/en\/1750-content-spoofing-vulnerability-using-a-naughty-string-that-affected-audit-trail-integrity\/","title":{"rendered":"$1,750 Content Spoofing Vulnerability Using a Naughty String That Affected Audit Trail Integrity"},"content":{"rendered":"\n

KacaTeknologi.com\/en<\/strong> \u2013 In bug bounty, not every valid finding comes from a highly complex technical issue. Sometimes, a simple and seemingly harmless input can lead to a real security vulnerability.<\/p>\n\n\n\n

In my case, the issue came from a single naughty string: a whitespace (\u201d \u201c).<\/p>\n\n\n\n

That trailing whitespace led to a Content Spoofing<\/strong> vulnerability, allowing me to impersonate other users and perform actions that appeared to come from them.<\/p>\n\n\n\n

What is Content Spoofing?<\/h2>\n\n\n\n

Generally speaking, Content Spoofing is a vulnerability where an attacker can inject arbitrary or misleading content to trick users into believing it is legitimate.<\/p>\n\n\n\n

For example, imagine I can change my username to match another user\u2019s identity. When I perform an action, other users may believe that the action was performed by the victim rather than me.<\/p>\n\n\n\n

If the system allows this confusion, the spoofing attack is successful.<\/p>\n\n\n\n

There are many types of content spoofing, but this article focuses on a simple username impersonation case.<\/p>\n\n\n\n

Why Input Validation Matters in Preventing Spoofing Attacks<\/h2>\n\n\n\n

During my testing, I came across a target that had a field called Account Display<\/strong>.<\/p>\n\n\n\n

This field initially appeared to have proper input validation. When I tried changing my display name from:<\/p>\n\n\n\n

\n

alqiattacker<\/p>\n<\/blockquote>\n\n\n\n

to another user\u2019s username:<\/p>\n\n\n\n

\n

alqivictim<\/p>\n<\/blockquote>\n\n\n\n

The application rejected my request and displayed this validation message: \u201cUsername cannot match other users\u2019 display names.<\/strong><\/em>\u201c<\/p>\n\n\n\n

This is expected behavior.<\/p>\n\n\n\n

Just like on Instagram or other social platforms, you typically cannot use another person\u2019s unique username because the application validates whether the value is already taken.<\/p>\n\n\n\n

If the username already exists, the server should reject the request. This is why input validation matters: to prevent impersonation attempts.<\/p>\n\n\n\n

So naturally, my next question was: Can this restriction be bypassed?<\/strong><\/p>\n\n\n\n

Bypassing Username Validation with a Trailing Whitespace<\/h2>\n\n\n\n

I initially tried several bypass techniques, including:<\/p>\n\n\n\n

    \n
  • Response manipulation<\/li>\n\n\n\n
  • Homograph attacks<\/li>\n<\/ul>\n\n\n\n

    Neither worked.<\/p>\n\n\n\n

    Then, almost by accident, I added a trailing whitespace to the end of the Account Display<\/code> value.<\/p>\n\n\n\n

    \"username<\/span><\/figure><\/div>\n\n\n\n

    Surprisingly, the server accepted the request.<\/p>\n\n\n\n

    At this point, I started asking a more important question:<\/p>\n\n\n\n

    What is the real impact of successfully changing my account display to another user\u2019s identity?<\/strong><\/p>\n\n\n\n

    To answer that, I needed to understand the application\u2019s business logic.<\/p>\n\n\n\n

    The Application Has an Audit Trail<\/h2>\n\n\n\n

    While reviewing the product documentation, I noticed the company has an\u00a0audit<\/strong><\/span> trail<\/strong> feature.<\/p>\n\n\n\n

    Naturally, I tested whether the audit trail itself could be modified directly.<\/p>\n\n\n\n

    I attempted to tamper with audit log records via API requests, but those endpoints were properly protected and returned a 403 Forbidden<\/strong> response.<\/p>\n\n\n\n

    So direct modification was not possible.<\/p>\n\n\n\n

    However, I had another angle: If I can spoof my identity, will the audit trail record my actions as the victim or as the real attacker?<\/span><\/p>\n\n\n\n

    Validating the Business Impact<\/h2>\n\n\n\n

    To test the impact, I performed several actions while using the spoofed display name:<\/p>\n\n\n\n

      \n
    • Uploading a file<\/li>\n\n\n\n
    • Updating a folder<\/li>\n\n\n\n
    • and many more<\/li>\n<\/ul>\n\n\n\n

      The results were interesting.<\/p>\n\n\n\n

      All actions were recorded under the victim\u2019s displayed identity instead of the attacker\u2019s.<\/p>\n\n\n\n

      In other words, although I was the one performing the actions, the audit trail visually suggested that the victim had performed them.<\/p>\n\n\n\n

      Why This Became a Real Security Issue<\/h3>\n\n\n\n

      The most impactful part was how the audit trail rendered user identity.<\/p>\n\n\n\n

      Instead of displaying:<\/p>\n\n\n\n

        \n
      • clickable profile links,<\/li>\n\n\n\n
      • user IDs,<\/li>\n\n\n\n
      • or unique identifiers,<\/li>\n<\/ul>\n\n\n\n

        The audit trail displayed only names.<\/p>\n\n\n\n

        That means administrators reviewing logs had no easy way to distinguish between:<\/p>\n\n\n\n

          \n
        • The legitimate victim, and<\/li>\n\n\n\n
        • The attacker using a spoofed display name.<\/li>\n<\/ul>\n\n\n\n

          As a result, the application\u2019s audit trail became functionally misleading.<\/p>\n\n\n\n