CVE-2025-1011 – A WebAssembly code generation bug in Mozilla pr... (How to Fix)

Q: How do I fix CVE-2025-1011?

1. Open affected application. 2. Go to Help > About Firefox/Thunderbird. 3. Allow automatic update or download latest version from mozilla.org. 4. Restart application.

Q: What is the severity of CVE-2025-1011?

CVE-2025-1011 has a CVSS score of 8.8 (HIGH). A WebAssembly code generation bug in Mozilla products could allow attackers to cause crashes and potentially execute arbitrary code. This affects Firefox versions below 135, Firefox ESR below 128.7, Thunderbird below 128.7, and Thunderbird below 135.

📋 TL;DR

A WebAssembly code generation bug in Mozilla products could allow attackers to cause crashes and potentially execute arbitrary code. This affects Firefox versions below 135, Firefox ESR below 128.7, Thunderbird below 128.7, and Thunderbird below 135.

💻 Affected Systems

Products:

Firefox
Firefox ESR
Thunderbird

Versions: Firefox < 135, Firefox ESR < 128.7, Thunderbird < 128.7, Thunderbird < 135

Operating Systems: All platforms supported by affected products

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations with WebAssembly enabled are vulnerable.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution leading to complete system compromise, data theft, or malware installation.

🟠

Likely Case

Application crash (denial of service) with potential for limited code execution in browser context.

🟢

If Mitigated

No impact if patched; crashes prevented if WebAssembly disabled.

🌐 Internet-Facing: HIGH - Browser-based vulnerabilities are directly exposed to internet content.

🏢 Internal Only: MEDIUM - Email clients (Thunderbird) could be exploited via malicious emails.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires WebAssembly execution; no public exploit available at disclosure.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firefox 135+, Firefox ESR 128.7+, Thunderbird 128.7+, Thunderbird 135+

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2025-07/

Restart Required: Yes

Instructions:

1. Open affected application. 2. Go to Help > About Firefox/Thunderbird. 3. Allow automatic update or download latest version from mozilla.org. 4. Restart application.

🔧 Temporary Workarounds

Disable WebAssembly

all

Prevents WebAssembly code execution, mitigating the vulnerability.

In Firefox/Thunderbird address bar, type about:config
Search for 'javascript.options.wasm'
Set to false

🧯 If You Can't Patch

Disable WebAssembly via about:config settings
Use application sandboxing or restricted execution environments

🔍 How to Verify

Check if Vulnerable:

Check application version against affected ranges in Help > About.

Check Version:

firefox --version or thunderbird --version

Verify Fix Applied:

Confirm version is Firefox 135+, Firefox ESR 128.7+, Thunderbird 128.7+, or Thunderbird 135+.

📡 Detection & Monitoring

Log Indicators:

Application crash logs with WebAssembly-related stack traces
Unexpected process termination

Network Indicators:

Suspicious WebAssembly module downloads
Unusual traffic to WebAssembly-heavy sites

SIEM Query:

source="firefox.log" AND ("crash" OR "segfault") AND "wasm"

📊 Metadata

CVE ID: CVE-2025-1011

CVSS v3 Score: 8.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CWE: CWE-94

EPSS Score: 0.35% exploit probability (57.1th percentile)

Published: February 4, 2025

Last Updated: November 3, 2025

🔗 References

https://bugzilla.mozilla.org/show_bug.cgi?id=1936454 Permissions Required
https://www.mozilla.org/security/advisories/mfsa2025-07/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-09/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-10/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-11/ Vendor Advisory
https://lists.debian.org/debian-lts-announce/2025/02/msg00005.html
https://lists.debian.org/debian-lts-announce/2025/02/msg00006.html

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