CVE-2025-49710: Mozilla Firefox Buffer Overflow Flaw

CVE-2025-49710 Overview

CVE-2025-49710 is a critical integer overflow vulnerability discovered in Mozilla Firefox's JavaScript engine, specifically within the OrderedHashTable component. This memory corruption flaw affects Firefox versions prior to 139.0.4 and could potentially allow remote attackers to compromise affected systems through specially crafted web content. The vulnerability exists in the hash table implementation used by Firefox's SpiderMonkey JavaScript engine, which processes untrusted content from websites visited by users.

Critical Impact

This integer overflow vulnerability in Firefox's JavaScript engine could allow attackers to achieve arbitrary code execution through maliciously crafted web pages, potentially leading to complete system compromise without user interaction beyond visiting a malicious website.

Affected Products

• Mozilla Firefox versions prior to 139.0.4
• Mozilla Firefox (all platforms - Windows, macOS, Linux)

Discovery Timeline

• 2025-06-11 - CVE-2025-49710 published to NVD
• 2025-06-16 - Last updated in NVD database

Technical Details for CVE-2025-49710

Vulnerability Analysis

This vulnerability represents a classic integer overflow condition (CWE-190) within the OrderedHashTable data structure used by Firefox's SpiderMonkey JavaScript engine. The OrderedHashTable is a fundamental component responsible for managing ordered collections in JavaScript, including Map and Set objects. When processing specially crafted JavaScript that manipulates these collections, the integer overflow can occur during size calculations or index computations.

Integer overflows in hash table implementations are particularly dangerous because they can lead to undersized memory allocations. When the application subsequently attempts to store data in the undersized buffer, heap corruption occurs, potentially enabling attackers to overwrite adjacent memory regions with controlled data.

The network-accessible nature of this vulnerability is especially concerning as exploitation requires no authentication or special privileges—users need only visit a malicious webpage containing the exploit code for the attack to succeed.

Root Cause

The root cause of CVE-2025-49710 lies in insufficient bounds checking during arithmetic operations within the OrderedHashTable implementation. When calculating memory allocation sizes or array indices, the code failed to properly validate that the resulting values remain within safe integer boundaries. This allows attackers to craft JavaScript operations that trigger integer wraparound, causing the computed size to become smaller than expected or even negative (interpreted as a large unsigned value).

In typical exploitation scenarios, an attacker would manipulate the hash table to grow to a size where subsequent calculations overflow, resulting in a heap buffer that is too small to hold the intended data. The detailed technical analysis is available in the Mozilla Bug Report #1970095.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no user interaction beyond navigating to a malicious website. An attacker could exploit this vulnerability through several methods:

1. Direct website hosting: Hosting malicious JavaScript on an attacker-controlled domain
2. Malvertising: Injecting exploit code through compromised advertising networks
3. Compromised legitimate sites: Injecting exploit code into vulnerable legitimate websites through XSS or other means
4. Phishing campaigns: Distributing links to exploitation pages via email or messaging platforms

The exploit would leverage the integer overflow in OrderedHashTable to corrupt heap memory, potentially achieving arbitrary code execution within the Firefox process context. For detailed technical information, refer to the Mozilla Security Advisory MFSA-2025-47.

Detection Methods for CVE-2025-49710

Indicators of Compromise

• Unexpected Firefox crashes or memory corruption errors when visiting specific websites
• Firefox process exhibiting abnormal memory consumption patterns
• Detection of malicious JavaScript attempting to create large Map or Set objects with specific size patterns
• Unusual child process spawning from the Firefox browser process

Detection Strategies

• Deploy browser isolation solutions to contain potential exploitation attempts
• Implement network-based intrusion detection signatures for known JavaScript exploitation patterns targeting hash table operations
• Monitor endpoint detection systems for anomalous Firefox process behavior including unexpected system calls or memory access violations
• Utilize content filtering to block access to known malicious domains distributing Firefox exploits

Monitoring Recommendations

• Enable crash reporting and analyze Firefox crash dumps for signs of heap corruption or exploitation attempts
• Monitor network traffic for connections to suspicious domains immediately following JavaScript execution anomalies
• Deploy behavioral analysis tools to detect post-exploitation activities such as payload downloads or lateral movement
• Review browser extension and add-on activity for potential exploit delivery mechanisms

How to Mitigate CVE-2025-49710

Immediate Actions Required

• Update Mozilla Firefox to version 139.0.4 or later immediately across all systems
• Enable automatic updates in Firefox to ensure timely patching of future vulnerabilities
• Consider temporarily using alternative browsers on high-value systems until the update is deployed
• Implement network-level protections such as web content filtering and browser isolation

Patch Information

Mozilla has addressed this vulnerability in Firefox version 139.0.4. The security fix was released as part of Mozilla Security Advisory MFSA-2025-47. Organizations should prioritize deployment of this update given the critical severity rating and network-accessible attack vector. The patch implements proper bounds checking for integer arithmetic operations within the OrderedHashTable implementation to prevent overflow conditions.

Workarounds

• Disable JavaScript execution in Firefox through about:config by setting javascript.enabled to false (note: this will significantly impact web browsing functionality)
• Deploy browser isolation solutions to execute web content in sandboxed environments
• Implement strict Content Security Policy headers on internal web applications to limit JavaScript execution sources
• Use network-level filtering to block access to known malicious domains and suspicious JavaScript content

# Firefox configuration via policies.json (for enterprise deployments)
# Place in Firefox installation directory under /distribution/policies.json
# This enables automatic updates to ensure timely patching
{
  "policies": {
    "DisableAppUpdate": false,
    "AppAutoUpdate": true,
    "ExtensionUpdate": true
  }
}