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Mozilla Issues Emergency Patch for Critical Zero-Day Vulnerability in Firefox and Thunderbird


September 13, 2023

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Mozilla Issues Emergency Patch for Critical Zero-Day Vulnerability in Firefox and Thunderbird

In a swift response to an emerging security threat, Mozilla has released emergency updates for its Firefox web browser and Thunderbird email client, aiming to patch a critical zero-day vulnerability.

The flaw, identified as CVE-2023-4863, affects the WebP image format and has reportedly been used in attacks. Mozilla's move comes a day after a similar update from Google, which patched the same vulnerability in its Chrome browser.

What We Know About the Vulnerability

The vulnerability is a heap buffer overflow issue that impacts the processing of WebP images. According to Mozilla's security advisory, "opening a malicious WebP image could lead to a heap buffer overflow in the content process. We are aware of this issue being exploited in other products in the wild."

The National Vulnerability Database (NVD) has categorized it as critical, stating that remote attackers could exploit this vulnerability to perform an out-of-bounds (OOB) memory write via a specially crafted HTML page.

Who Discovered the Flaw

The critical flaw was reported by Apple Security Engineering and Architecture (SEAR) and the Citizen Lab at the University of Toronto's Munk School. Their efforts have contributed to mitigating a significant risk to users across different platforms.

Affected Versions and Updates

Mozilla has addressed the vulnerability in the following software versions:

  • Firefox 117.0.1
  • Firefox ESR 115.2.1
  • Firefox ESR 102.15.1
  • Thunderbird 102.15.1
  • Thunderbird 115.2.2

Implications and Next Steps

The quick action from Mozilla belies the severity of the vulnerability, especially as it has been exploited in the wild. Rapid responses like this are crucial for maintaining user trust and security as attackers grow more sophisticated.

Users are urged to update to the latest versions to mitigate the risks associated with this critical flaw. Failure to do so could result in arbitrary code execution, letting attackers seize control of affected systems.

As this vulnerability affects multiple browsers, including Google's Chrome, it emphasizes the cross-platform nature of such security risks and the importance of collective action in the tech community.

Specialized software like Bitdefender Ultimate Security can protect you from zero-day exploits and other digital threats. Key features include:

  • Continuous, comprehensive detection and protection against viruses, Trojans, worms, zero-day exploits, spyware, ransomware, rootkits and other cyberthreats
  • Vulnerability assessment module that scans your system for security shortcomings and suggests the best fix
  • Network-threat prevention technology that identifies and blocks suspicious network-level activities such as sophisticated exploits, malware- and botnet-related URLS and brute-force attacks
  • Behavioral detection module that continuously scans active apps and acts instantly upon detecting suspicious behavior




Vlad's love for technology and writing created rich soil for his interest in cybersecurity to sprout into a full-on passion. Before becoming a Security Analyst, he covered tech and security topics.

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