CVE-2021-38498 in Firefox
Summary
by MITRE • 11/03/2021
During process shutdown, a document could have caused a use-after-free of a languages service object, leading to memory corruption and a potentially exploitable crash. This vulnerability affects Firefox < 93, Thunderbird < 91.2, and Firefox ESR < 91.2.
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Analysis
by VulDB Data Team • 08/17/2025
This vulnerability represents a critical memory safety issue that emerged during the process shutdown phase of affected Mozilla applications. The flaw manifests as a use-after-free condition involving a language service object, which occurs when the application attempts to access memory that has already been deallocated. Such conditions are particularly dangerous because they can lead to unpredictable behavior and potential code execution opportunities for malicious actors. The vulnerability affects multiple Mozilla products including Firefox versions prior to 93, Thunderbird versions prior to 91.2, and Firefox ESR versions prior to 91.2, indicating a widespread impact across the Mozilla ecosystem.
The technical nature of this vulnerability aligns with common software security weaknesses classified under CWE-416, which specifically addresses use-after-free conditions. During normal application operation, language service objects are typically managed through proper memory allocation and deallocation cycles. However, during the shutdown sequence, the application's memory management logic fails to properly handle the cleanup of these objects, creating a window where freed memory can be accessed. This scenario represents a classic memory corruption vulnerability that can be exploited through carefully crafted input that triggers the problematic code path during application termination.
The operational impact of this vulnerability extends beyond simple application crashes, as it creates a potential exploit vector that could allow remote code execution. Attackers could potentially craft malicious documents that, when processed and subsequently cause the application to shut down, would trigger the use-after-free condition. This type of vulnerability is particularly concerning because it can be exploited during normal user activities such as opening documents, visiting websites, or processing email messages. The timing of the vulnerability during shutdown makes it especially dangerous since users may be less vigilant during this phase of application use, and the exploitation could occur without direct user interaction beyond triggering the initial document processing.
Security practitioners should prioritize immediate patching of affected versions, as this vulnerability falls under the category of remotely exploitable memory corruption flaws that can lead to full system compromise. Organizations should implement comprehensive patch management programs to address this vulnerability across all affected Mozilla applications. The mitigation strategy should include not only updating to patched versions but also monitoring for potential exploitation attempts through network traffic analysis and endpoint detection systems. Additionally, users should be educated about the importance of keeping their applications updated, particularly since this vulnerability can be exploited through legitimate user activities such as document processing or web browsing. The ATT&CK framework categorizes this type of vulnerability under software exploitation techniques, specifically targeting memory corruption as a means to achieve arbitrary code execution.