AnQiCMS provides rich and powerful template tags and filters to help us flexibly display website content. Among them,replaceA filter is a very practical text processing tool that allows us to replace specific keywords in strings with new content.Use it properly on the front-end page to enhance the flexibility and maintenance efficiency of the content.replaceThe filter may also bring some security risks that should not be ignored.

replaceFilter introduction

First, let's take a look back atreplaceBasic function of the filter. In the template syntax of AnQiCMS,replaceThe usage of the filter is usually{{ obj|replace:"旧关键词,新关键词" }}。Its function is toobj

For example, if we want to replace all occurrences of "AnQi" in a paragraph, we can use it like this:{{"欢迎使用安企CMS"|replace:"安企,AnQi"}}，This will be displayed as “Welcome to AnQiCMS”. It looks simple and very useful.

The root cause of safety hazards: traps of dynamic content and automatic escaping

replaceThe filter itself is a string manipulation tool and does not directly cause security issues.The real risk lies in the source of the 'obj' (original content) and the 'new keywords', as well as the automatic escaping mechanism of the front-end template engine.AnQiCMS's template engine defaults to escaping HTML entities in the output content, which is a very important security feature that can effectively prevent cross-site scripting (XSS) attacks.<script>alert('XSS')</script>，默认情况下它会被转义为 English&lt;script&gt;alert(&#39;XSS&#39;)&lt;/script&gt;，从而无法被浏览器执行。

然而，当我们在 Englishreplace过滤器处理后的内容上，进一步使用了 EnglishsafeFiltering, this default security will be lifted.safeThe filter's purpose is to inform the template engine that this content is 'safe', and does not need to be HTML-escaped; it can be output as raw HTML directly. It is in this situation that ifreplaceThe filter failed to clear malicious code or did not introduce it, which could lead to serious security issues.

Common security risk scenarios

  1. Cross-site Scripting (XSS)This is one of the most common and most harmful security issues on the front-end page.When an attacker can inject malicious scripts into a webpage and have other users execute them, XSS may occur.replaceThe following situations in the context of the filter may lead to XSS:

    • Malicious content replacement injection:IfreplaceThe 'new keyword' parameter of the filter comes from user input or the original contentobjThe input includes user input that has not been strictly disinfected, an attacker may carefully construct a string containing JavaScript code. For example, an attacker submits a comment, the content of which includesalert('XSS')IfreplaceOperation not recognized and this code was not removed, but it was used again afterwards|safeFilter, this code may be executed when other users access the page
    • HTML structure and attribute injection:The attacker may attempt to replace some tag attributes, such as replacinghref="#"withhref="javascript:alert('XSS')".replaceThe filter is abused when processing these attributes, and the final output content is not escaped (because it uses|safeThen, clicking this link will execute malicious scripts.
    • Unverified dynamic data source:Assumeobjor新关键词from a third-party API interface, and these interfaces' data has not been strictly checked for security, which may contain malicious HTML or JavaScript fragments. IfreplaceAfter processing this content, the template marks it assafeIf the output is, then this malicious content will be displayed directly in the user's browser.

  2. Content Spoofing/DefacementAlthough it does not belong to the strict sense of code execution vulnerabilities, content tampering is also destructive to the reputation and user trust of the website.

    • Replace brand words or key information:The attacker may control through some method (such as exploiting a background content editing vulnerability)replaceIn the filter.旧关键词or新关键词.For example, replace the "official customer service" on the website with "contact scammer customer servicereplacecontrol of parameters, but once implemented, through the frontendreplaceFilter outputs without discrimination, which can cause great misdirection to users.

Preventive measures and **practice

To effectively avoidreplaceSecurity risks brought by filters, we need to strengthen protection from multiple levels:

  1. Be vigilantsafeHow to use the filter:This is the most core defense point. Unless you are 100% sure that the content is strictly disinfected and free of any potential risks as HTML, it should be avoided.replaceuse it after the filter|safe.In most cases, it is safer to let AnQiCMS's template engine automatically perform HTML escaping.If you indeed need to output raw HTML (such as content generated by rich text editors), make sure that the content has been strictly sanitized and filtered on the server side (backend) before saving it to the database, removing all possible malicious scripts and unsafe HTML tags.

  2. Strictly review all input sources:Any data originating from user submissions, URL parameters, file uploads, or third-party APIs should be considered "untrusted" data. When usingreplaceFilter these data thoroughly before processing them. This includes, but is not limited to, removing HTML tags, checking URL protocols (only allowinghttp/https）、Limit input length, validate data format, etc.

  3. Front-end and back-end double verification:It is not enough to validate and filter on the front-end.All data submitted by users must be strictly validated on the server side.Even though some malicious content has been filtered out on the front-end, the back-end must still perform verification and filtering to prevent experienced attackers from bypassing the front-end defenses.

  4. ClearreplaceApplication scenarios: replaceThe safest use of the filter is to process static, text content that developers have complete control over, or to make fine adjustments on data that has already been strictly secured.For example, replace a fixed misspelling, or format data with a known structure.Avoid using it for directly modifying or combining HTML structures from untrusted sources.

  5. Regular code review and security audit:The developer should regularly review template code, especially those that usereplacefilters andsafeparts of filters. Check the data flow to ensure that every step from input to output conforms to safety standards.

Summary

AnQiCMSreplaceFilter is a powerful text processing tool that can implement flexible content adjustment on the front-end page.But its power also comes with potential risks.|safeFilter）at. By adhering to secure practices such as strict input validation and cautious usesafeFilter and regular code reviews, we can fully utilizereplaceThe advantages of the filter, while ensuring the security and stability of the website.

Common Questions (FAQ)

  1. AnQiCMSreplaceDoes the filter come with HTML encoding functionality? replaceThe filter itself does not perform HTML escaping.It simply performs a string replacement operation.replaceFiltering is done, but before the content is finally displayed on the page. So, unless you explicitly inreplaceuse it after the filter|safeFilter, the content will be escaped.

2.