What are the critical vulnerabilities fixed in Firefox 141 and why should you update immediately?

Table of Contents

• What’s This About?
• Why Is Firefox 141 Important for Cybersecurity?
• CVE-2025-8027: Critical Flaw in JavaScript Return Value Handling
• CVE-2025-8028: WebAssembly Branch Truncation on ARM64
• CVE-2025-8036: DNS Rebinding & CORS Security Bypass
• CSP Violations: CVE-2025-8032 & CVE-2025-8031
• CVEs Affecting Memory Safety
• Firefox for Android: Mobile-Specific Fixes
• Why You Should Update Immediately
• Firefox 141 Key Vulnerabilities
• Conclusion
• Frequently Asked Questions (FAQs)

What’s This About?

Mozilla has rolled out Firefox 141, a critical security update fixing 17 serious vulnerabilities that could lead to arbitrary code execution, security bypasses, and memory corruption. Among the vulnerabilities are flaws in the JavaScript engine, WebAssembly implementation, and Cross-Origin Resource Sharing (CORS) security model.

This blog explains the key vulnerabilities patched, why they’re dangerous, and why immediate updates are crucial for Firefox users—across both desktop and mobile platforms.

Why Is Firefox 141 Important for Cybersecurity?

With cyberattacks growing more sophisticated, even browsers are now prime targets for zero-day exploits. Firefox 141 addresses critical CVEs that attackers could exploit to gain access to sensitive data or take control of devices remotely—especially via malicious websites.

If you're using Firefox or Thunderbird, updating to the latest version is no longer optional—it's urgent.

CVE-2025-8027: Critical Flaw in JavaScript Return Value Handling

Mozilla patched a critical vulnerability in its JavaScript JIT (Just-in-Time) engine:

• What happened: IonMonkey-JIT wrote only 32 bits of a 64-bit value, while Baseline-JIT attempted to read the full 64 bits.

• Impact: This mismatch caused memory inconsistencies, which attackers could manipulate to execute arbitrary code.

• Who found it: Security researcher Nan Wang.

  
  

Risk Level: High
Attack Surface: Malicious JavaScript on a webpage

CVE-2025-8028: WebAssembly Branch Truncation on ARM64

Another critical flaw affected ARM64 systems running WebAssembly:

• What happened: A br_table instruction with too many entries caused label truncation, leading to incorrect branching.

• Impact: Could allow attackers to hijack execution flow in compiled WebAssembly apps.

• Discovered by: Gary Kwong

Risk Level: High
Attack Surface: Apps using WebAssembly modules

CVE-2025-8036: DNS Rebinding & CORS Security Bypass

Firefox’s Cross-Origin Resource Sharing (CORS) cache mechanism was misused in a DNS rebinding attack:

• What happened: CORS preflight responses were cached across IP changes, enabling attackers to bypass origin checks.

• Risk: Compromises web apps that rely on same-origin policy for protection.

• Reported by: Viktor Bocz

CSP Violations: CVE-2025-8032 & CVE-2025-8031

Two key issues affected Firefox’s Content Security Policy (CSP):

• CVE-2025-8032: Allowed XSLT documents to sidestep CSP restrictions.

• CVE-2025-8031: Leaked HTTP Basic Auth credentials via improperly sanitized CSP reports.

These bugs demonstrate how standards-compliant features, when poorly implemented, become threat vectors.

CVEs Affecting Memory Safety

Mozilla also resolved several memory corruption vulnerabilities, including:

Most were detected by the Mozilla Fuzzing Team, showing how automated fuzzing tools are essential to securing modern codebases.

Firefox for Android: Mobile-Specific Fixes

Two issues were patched specifically for Android users:

• CVE-2025-8041: Long URLs were truncated, hiding potentially dangerous query strings.

• CVE-2025-8042: Sandboxed iframes could improperly initiate downloads—a bypass of user-consent models.

 These vulnerabilities remind us that mobile browsers require just as much scrutiny as desktop ones.

Why You Should Update Immediately

Attackers actively monitor browser changelogs and reverse-engineer patches to develop new exploits. Delaying updates—especially when vulnerabilities allow remote code execution—is an open invitation for compromise.

How to Update:
Open Firefox → Menu → Help → About Firefox → It will auto-update.

Firefox 141 Key Vulnerabilities

Conclusion

Firefox 141 is more than just a performance or UI update—it’s a security lifeline. With attackers now exploiting flaws in JIT engines, CORS logic, and memory management, browsers are frontline battlegrounds in cyber warfare.

Updating your browser today isn't about convenience—it's about survival in a threat-rich digital world.

Stay patched. Stay safe. Stay one step ahead.

Frequently Asked Questions (FAQs)

What is Firefox 141?

Firefox 141 is the latest version of Mozilla’s web browser released in July 2025, containing significant security patches.

Why is Firefox 141 considered a critical update?

It fixes 17 vulnerabilities, including those that could lead to arbitrary code execution or security bypasses.

What are the most severe vulnerabilities fixed in Firefox 141?

CVE-2025-8027 and CVE-2025-8028 are among the most severe, targeting JavaScript engine and WebAssembly processing.

What is CVE-2025-8027?

A memory inconsistency bug where only 32 bits of a 64-bit return value were written to the stack, leading to possible code execution.

Who discovered CVE-2025-8027?

Security researcher Nan Wang.

What is CVE-2025-8028?

A vulnerability in ARM64 systems where br_table instructions in WebAssembly could be miscomputed, allowing branch hijacking.

Who reported CVE-2025-8028?

Security researcher Gary Kwong.

What does “arbitrary code execution” mean?

It means an attacker could run unauthorized code on your system through a browser exploit.

What are DNS rebinding attacks mentioned in the update?

DNS rebinding tricks the browser into connecting to local systems by changing IPs behind domain names.

How does CVE-2025-8036 affect CORS?

Firefox cached preflight responses even when IP addresses changed, allowing cross-origin requests to be spoofed.

What is CORS?

Cross-Origin Resource Sharing — a web standard for restricting cross-domain data access.

What are CSP bypasses in Firefox 141?

Flaws like CVE-2025-8032 and CVE-2025-8031 allowed XSLT and basic auth leaks to bypass browser CSP policies.

What is CVE-2025-8031?

A flaw that exposed HTTP Basic Auth credentials in CSP reports.

What does CSP stand for?

Content Security Policy — a browser mechanism to prevent content injection attacks.

What kind of memory safety issues were patched?

Memory corruption bugs across Firefox and Thunderbird, including CVE-2025-8044 and CVE-2025-8034.

How can memory corruption be exploited?

Attackers can manipulate memory to execute malicious code or crash the browser.

Were mobile users affected by these vulnerabilities?

Yes, Firefox for Android had issues like unsafe iframe downloads and poor URL truncation visibility.

What is CVE-2025-8042?

A sandboxed iframe in Firefox Android could initiate unintended downloads.

Who maintains security for Firefox?

The Mozilla Security Team and contributors including fuzzing researchers.

What is Mozilla Fuzzing?

An automated method to find bugs by feeding unexpected or random data into the browser.

How can I check if I’m using Firefox 141?

Go to Menu → Help → About Firefox — it will show the current version.

What platforms are affected by these vulnerabilities?

Windows, macOS, Linux, and Android versions of Firefox.

Should enterprises be concerned about this update?

Yes. Organizations with custom web apps or high-traffic web usage are at risk without the patch.

Is Firefox 141 available for download now?

Yes, it was officially released on July 22, 2025.

What happens if I don’t update Firefox?

You remain vulnerable to attacks that can steal data, inject malware, or bypass browser protections.

Are Thunderbird users also affected?

Yes, some vulnerabilities were shared with Mozilla Thunderbird and have been patched.

Can antivirus software protect against these Firefox bugs?

Not completely. These are browser-level exploits that require patching to mitigate effectively.

How do I enable auto-update in Firefox?

Go to Settings → General → Firefox Updates and enable automatic updates.

Does Firefox 141 fix all past security issues?

It addresses 17 newly reported issues. Past versions should already have their own updates.

Where can I read the full Mozilla advisory?

Visit https://www.mozilla.org/security/advisories and look for MFSA 2025-56.