CVE-2017-5445 in Firefox
Summary
by MITRE
A vulnerability while parsing "application/http-index-format" format content where uninitialized values are used to create an array. This could allow the reading of uninitialized memory into the arrays affected. This vulnerability affects Thunderbird < 52.1, Firefox ESR < 45.9, Firefox ESR < 52.1, and Firefox < 53.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-5445 represents a critical memory safety issue within Mozilla's browser and email client software ecosystems. This flaw manifests specifically during the parsing of "application/http-index-format" content, which is a MIME type used for representing HTTP index information in web applications and email messages. The vulnerability stems from improper memory management practices that allow uninitialized values to be utilized in array creation operations, potentially exposing sensitive data through memory disclosure attacks. The affected software versions include Thunderbird versions prior to 52.1, Firefox Extended Support Release versions before 45.9 and 52.1, and standard Firefox versions before 53, indicating this vulnerability impacted a significant portion of the user base during its active period.
The technical implementation of this vulnerability falls under the category of uninitialized memory access, which is classified as CWE-457: Use of Uninitialized Variable. The flaw occurs when the application processes HTTP index format content and attempts to create arrays based on data that has not been properly initialized. This uninitialized memory typically contains remnants of previous operations or system data, which can include sensitive information such as cryptographic keys, passwords, session tokens, or other confidential data. When the parsing logic creates arrays using these uninitialized values, the memory contents are inadvertently copied into the arrays, potentially exposing portions of the application's memory space to unauthorized access. This type of vulnerability is particularly dangerous because it can lead to information disclosure attacks that may compromise user privacy and system security.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable sophisticated attack vectors that leverage the exposure of uninitialized memory contents. Attackers could potentially exploit this weakness to gain insights into memory layouts, application behavior, or even extract sensitive data from the affected applications. The vulnerability affects both web browsers and email clients, making it a multi-vector threat that could be exploited through various attack surfaces including web pages, email attachments, or HTTP responses. This type of memory corruption vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, where attackers might use memory disclosure to gather information about target systems before launching more sophisticated attacks. The widespread nature of the affected software versions suggests that many users were potentially exposed to this risk for extended periods, particularly those running older versions of Firefox ESR or Thunderbird.
Mitigation strategies for CVE-2017-5445 primarily focus on immediate software updates and patches provided by Mozilla to address the uninitialized memory access issue. Organizations should prioritize updating all affected systems to the latest versions of Firefox, Thunderbird, and their respective ESR releases to eliminate the vulnerability. Additionally, implementing network monitoring and intrusion detection systems can help identify potential exploitation attempts targeting this specific vulnerability. Security teams should also consider deploying application firewalls or content filtering solutions that can block or sanitize HTTP index format content when it flows through network boundaries. The vulnerability serves as a reminder of the importance of proper memory initialization practices in software development, particularly for applications handling external data inputs. Organizations should also conduct regular security assessments of their browser and email client configurations to ensure that all security patches are properly applied and that legacy systems are appropriately managed or decommissioned to prevent exploitation of known vulnerabilities.