CVE-2025-4919 is a high-severity vulnerability affecting Mozilla products, specifically Firefox and Thunderbird. This vulnerability allows an attacker to perform an out-of-bounds read or write on a JavaScript object by confusing array index sizes. The vulnerability impacts versions of Firefox prior to 138.0.4 and Thunderbird prior to 128.10.2. With a CVSS score of 8.8, this flaw poses significant risks to organizations relying on these applications.
The issues arise from improper bounds checking, leading to potential data corruption or unauthorized access. Organizations using affected versions should prioritize applying vendor patches to mitigate the risk associated with this vulnerability. Due to the critical nature of this flaw, immediate action is required to secure systems against potential exploitation.
Risk to organizations includes high confidentiality, integrity, and availability impacts. Attackers may leverage this vulnerability to compromise sensitive data, making it imperative for security teams to address this vulnerability promptly.
Given the high exploitability score and the absence of known exploits at this time, defenders should remain vigilant. Organizations should prioritize patching immediately to reduce exposure to potential attacks stemming from this vulnerability.
Vulnerability Details
The official description of CVE-2025-4919 states that an attacker was able to perform an out-of-bounds read or write on a JavaScript object by confusing array index sizes. This vulnerability affects Firefox versions earlier than 138.0.4, Firefox ESR versions earlier than 128.10.1, and Thunderbird versions earlier than 128.10.2. It has been classified under CWE-125 (Out-of-bounds Read) and CWE-787 (Out-of-bounds Write).
The CVSS 3.1 score for this vulnerability is 8.8, classified as high severity. The attack vector is network-based, requiring user interaction, with a low attack complexity. The impacts of this vulnerability include high confidentiality, integrity, and availability concerns.
This vulnerability was published on May 17, 2025, and has since been modified. Organizations should keep abreast of updates provided by Mozilla regarding this vulnerability.
Technical Analysis
The root cause of this vulnerability is linked to improper handling of array index sizes within JavaScript objects, which can lead to out-of-bounds accesses. This condition can potentially be exploited over a network, allowing an attacker to manipulate the application’s memory management.
The attack complexity is assessed as low due to the reliance on user interaction, where users may inadvertently trigger the exploit by visiting a malicious site or engaging with compromised content.
There are no privileges required for the attack, as the vulnerability can be exploited without prior authentication. The potential consequences include a complete compromise of confidentiality, integrity, and availability of the affected systems.
Risk & Impact Analysis
Real-world deployment of this vulnerability poses a significant risk to organizations. Attackers may leverage the out-of-bounds read/write capabilities to corrupt data or gain unauthorized access to sensitive information.
The potential blast radius is substantial, as both Firefox and Thunderbird are widely used applications across various platforms. The urgency for organizations to patch this vulnerability is high, given its CVSS score of 8.8 and the potential for severe impacts.
Organizations should assess their exposure to this vulnerability and prioritize remediation efforts in their patch management processes. The risk assessment should reflect the current threat landscape and the critical nature of the applications affected.
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The vulnerability affects the following versions: Firefox < 138.0.4, Firefox ESR < 128.10.1, Firefox ESR < 115.23.1, Thunderbird < 128.10.2, and Thunderbird < 138.0.2. Organizations are advised to upgrade to the latest patched versions to mitigate this vulnerability.
Mitigation & Remediation
Organizations should immediately apply the latest security updates from Mozilla for Firefox and Thunderbird to address this vulnerability. For Firefox, upgrade to version 138.0.4 or later. For Firefox ESR, upgrade to version 128.10.1 or later. For Thunderbird, upgrade to version 128.10.2 or later.
If a patch is unavailable, organizations should consider implementing configuration hardening, such as restricting JavaScript execution on untrusted websites. Network controls can also be established to limit exposure until patches are applied.
Organizations may also benefit from conducting a thorough review of their application security practices and ensuring they have a solid incident response plan in place.
For further insights into continuous security testing, organizations should refer to continuous penetration testing to validate their defenses.
Detection Guidance
Organizations should monitor logs for any indicators of unusual behavior that may suggest exploitation attempts. Specific attention should be given to network traffic patterns that might indicate attempts to trigger the vulnerability.
Behavioral anomalies in user interactions, particularly those involving JavaScript execution, should also be closely examined. System changes, especially those resulting from untrusted content access, should be logged and analyzed.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2025-4919 highlights the persistent challenge of ensuring secure JavaScript execution in web applications. As more functionalities are integrated into web browsers, the risk associated with JavaScript vulnerabilities continues to grow.
This vulnerability represents a trend towards increasingly sophisticated exploitation techniques targeting widely-used applications. Security teams should take this as a lesson to reinforce their defenses and remain vigilant against emerging threats.
Organizations should consider adopting comprehensive security assessments such as application security assessments to identify potential vulnerabilities and strengthen their security posture.
Additionally, following a structured penetration testing methodology can help organizations stay ahead of potential threats.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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