CVE-2025-4082: Mozilla Firefox Privilege Escalation Bug

CVE-2025-4082 Overview

CVE-2025-4082 is an out-of-bounds read vulnerability [CWE-125] in Mozilla Firefox and Thunderbird. The flaw resides in the WebGL shader handling logic. Attackers can trigger the issue by modifying specific WebGL shader attributes, causing the browser to read memory outside the intended bounds. When chained with other vulnerabilities, the leaked memory contents could be used to escalate privileges. The Thunderbird impact is limited to the macOS build. Mozilla addressed the issue in Firefox 138, Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, and Thunderbird 128.10.

Critical Impact

Out-of-bounds memory read in WebGL shader processing enables information disclosure that, when combined with additional flaws, supports privilege escalation against macOS Thunderbird users and Firefox users across platforms.

Affected Products

• Mozilla Firefox versions prior to 138
• Mozilla Firefox ESR versions prior to 128.10 and 115.23
• Mozilla Thunderbird versions prior to 138 and 128.10 (Thunderbird impact limited to macOS)

Discovery Timeline

• 2025-04-29 - CVE-2025-4082 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2025-4082

Vulnerability Analysis

The vulnerability stems from improper bounds checking in the WebGL implementation shared by Firefox and Thunderbird. WebGL exposes GPU functionality to web content through JavaScript bindings that compile and execute shader programs. When an attacker modifies specific shader attributes, the rendering pipeline reads beyond the allocated buffer for that attribute. This out-of-bounds read can expose adjacent process memory contents to attacker-controlled JavaScript.

On its own, the issue is an information disclosure primitive. Chained with a memory corruption or sandbox escape vulnerability, the leaked addresses or data can defeat Address Space Layout Randomization (ASLR) and assist in escalating privileges. Mozilla notes the Thunderbird exposure is limited to macOS because the affected WebGL code path is only reachable in that build configuration.

Root Cause

The root cause is missing or insufficient validation of shader attribute parameters before they are used to index into GPU buffer memory. The WebGL implementation trusts attribute metadata that an attacker can manipulate, allowing reads past the legitimate buffer boundary. The condition maps to CWE-125 (Out-of-bounds Read).

Attack Vector

Exploitation requires the victim to load attacker-controlled web content in Firefox or, in the case of Thunderbird on macOS, to render content that exercises the WebGL code path. The attack is network-reachable with no privileges or user interaction beyond visiting the malicious page. Successful exploitation does not on its own execute code, but the leaked memory supports follow-on exploitation when paired with a separate corruption bug.

No public proof-of-concept exploit, ExploitDB entry, or CISA KEV listing is associated with this CVE. Technical specifics are tracked in Mozilla Bug Report #1937097.

Detection Methods for CVE-2025-4082

Indicators of Compromise

• Firefox or Thunderbird processes loading remote WebGL content from low-reputation domains shortly before unexpected crashes or renderer process restarts.
• Browser telemetry showing repeated shader compilation failures or WEBGL_* errors from a single origin.
• macOS Thunderbird rendering HTML messages that reference external WebGL resources, which is uncommon for legitimate email.

Detection Strategies

• Inventory installed Firefox, Firefox ESR, and Thunderbird versions across endpoints and flag any builds below 138, ESR 128.10, ESR 115.23, or Thunderbird 128.10.
• Monitor process telemetry for unexpected child processes or memory access violations originating from firefox or thunderbird binaries.
• Inspect proxy and DNS logs for users browsing to pages that load WebGL shaders from untrusted third-party domains.

Monitoring Recommendations

• Enable browser crash reporting and aggregate renderer crash signatures to identify clusters tied to WebGL.
• Alert on outbound connections from thunderbird on macOS to non-mail infrastructure, which may indicate remote content loading.
• Track endpoints that fail to receive Mozilla auto-updates and surface them for manual remediation.

How to Mitigate CVE-2025-4082

Immediate Actions Required

• Upgrade Firefox to version 138 or later and Firefox ESR to 128.10 or 115.23 as applicable.
• Upgrade Thunderbird to 138 or 128.10, prioritizing macOS endpoints where the vulnerability is reachable.
• Verify that automatic updates are enabled in managed deployments and confirm the rollout reaches all users.

Patch Information

Mozilla released fixes in Firefox 138, Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, and Thunderbird 128.10. Refer to the vendor advisories for build-specific details: MFSA-2025-28, MFSA-2025-29, MFSA-2025-30, MFSA-2025-31, and MFSA-2025-32. Debian users should review the Debian LTS Announcement.

Workarounds

• Disable WebGL in Firefox by setting webgl.disabled to true in about:config until patches are applied.
• On macOS Thunderbird, disable remote content rendering in message preferences to block the WebGL code path.
• Restrict access to untrusted websites through enterprise proxy or DNS filtering for unpatched hosts.

# Configuration example: disable WebGL via Firefox enterprise policy (policies.json)
{
  "policies": {
    "Preferences": {
      "webgl.disabled": {
        "Value": true,
        "Status": "locked"
      }
    }
  }
}