CVE-2026-10702: Firefox JIT RCE Vulnerability Explained

CVE-2026-10702 Overview

CVE-2026-10702 is a Just-In-Time (JIT) miscompilation vulnerability in the JavaScript Engine of Mozilla Firefox. The flaw resides in the JIT component and is classified as a type confusion issue under [CWE-843]. Mozilla addressed the defect in Firefox 151.0.3 as part of security advisory MFSA-2026-54.

Exploitation requires user interaction, such as visiting a malicious web page that triggers the affected code generation path. Successful exploitation can produce limited availability impact within the renderer process. Mozilla has not reported in-the-wild exploitation, and EPSS data indicates a low predicted exploitation probability.

Critical Impact

A crafted JavaScript payload can trigger JIT miscompilation in Firefox versions prior to 151.0.3, leading to type confusion and potential renderer crashes or memory corruption.

Affected Products

• Mozilla Firefox versions prior to 151.0.3
• Mozilla Firefox JavaScript Engine: JIT component
• Downstream browsers embedding the affected SpiderMonkey JIT build

Discovery Timeline

• 2026-06-02 - CVE-2026-10702 published to NVD
• 2026-06-03 - Last updated in NVD database

Technical Details for CVE-2026-10702

Vulnerability Analysis

The vulnerability stems from a miscompilation in Firefox's JIT compiler within the SpiderMonkey JavaScript engine. JIT compilers translate hot JavaScript paths into native machine code using inferred type assumptions. When the compiler emits incorrect machine code for a given input, the generated code can operate on values whose actual runtime types differ from the types the optimizer assumed.

This behavior aligns with [CWE-843], Access of Resource Using Incompatible Type (Type Confusion). The result is that native code may read or manipulate JavaScript values as if they were a different type, producing undefined behavior in the renderer process. The attack vector is network-based and requires the victim to load attacker-controlled content in the browser.

Root Cause

The root cause is an incorrect optimization decision in the JIT pipeline that produces machine code inconsistent with the runtime representation of one or more JavaScript values. Mozilla resolved the defect in the JIT compilation logic shipped in Firefox 151.0.3. Refer to Mozilla Bug Report #2040903 for the upstream tracking record.

Attack Vector

An attacker hosts a web page containing JavaScript designed to drive the JIT into the miscompiled code path. When a user visits the page with a vulnerable Firefox build, the JIT emits faulty native code that executes against mistyped values. The immediate observable outcome is a crash or denial-of-service condition in the content process, consistent with the limited availability impact reflected in the CVSS metrics.

No public proof-of-concept exploit code is currently associated with this CVE. For technical specifics, see the Mozilla Security Advisory MFSA-2026-54.

Detection Methods for CVE-2026-10702

Indicators of Compromise

• Unexpected content-process crashes in Firefox with stack frames originating in IonMonkey or Warp JIT modules
• Browser telemetry showing repeated MOZ_CRASH events tied to JavaScript execution on specific origins
• Outbound connections from endpoints to recently registered domains immediately preceding browser crash events

Detection Strategies

• Inventory Firefox installations and flag any version below 151.0.3 for remediation tracking
• Inspect crash reporter submissions for signatures associated with JIT-generated code regions
• Correlate browser process crashes with web navigation logs to identify potentially malicious URLs

Monitoring Recommendations

• Forward Firefox crash telemetry and endpoint process termination events to a central logging platform
• Alert on repeated Firefox renderer crashes on the same host within a short window
• Monitor web proxy logs for users navigating to uncategorized or low-reputation domains followed by browser instability

How to Mitigate CVE-2026-10702

Immediate Actions Required

• Upgrade all Firefox installations to version 151.0.3 or later across managed endpoints
• Validate that automatic update channels are enabled and reaching client systems
• Restart browser sessions after deployment to ensure the patched JIT binary is loaded

Patch Information

Mozilla fixed CVE-2026-10702 in Firefox 151.0.3. Administrators should obtain the update directly from Mozilla or through enterprise distribution channels. Full details are available in Mozilla Security Advisory MFSA-2026-54.

Workarounds

• Restrict access to untrusted web content through enterprise web filtering until patching is complete
• Disable the JIT compiler temporarily by setting javascript.options.ion and javascript.options.baselinejit to false in about:config, accepting the performance trade-off
• Apply strict Content Security Policy headers on internal applications to limit exposure to third-party scripts

# Configuration example: enforce Firefox auto-update policy via enterprise policies.json
{
  "policies": {
    "DisableAppUpdate": false,
    "AppAutoUpdate": true,
    "OverrideFirstRunPage": "",
    "Preferences": {
      "javascript.options.ion": { "Value": false, "Status": "locked" },
      "javascript.options.baselinejit": { "Value": false, "Status": "locked" }
    }
  }
}