CVE-2023-6207 in Thunderbird
Summary
by MITRE • 11/21/2023
Ownership mismanagement led to a use-after-free in ReadableByteStreams This vulnerability affects Firefox < 120, Firefox < 115.5, and Thunderbird < 115.5.0.
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Analysis
by VulDB Data Team • 06/19/2025
The vulnerability identified as CVE-2023-6207 represents a critical use-after-free condition within the ReadableByteStreams implementation of Mozilla Firefox and Thunderbird applications. This issue stems from improper ownership management during the handling of asynchronous data streams, creating a scenario where memory resources become accessible after they have been freed. The flaw manifests when the application processes readable byte streams that are subject to concurrent access patterns, leading to potential memory corruption that could be exploited by malicious actors.
The technical root cause of this vulnerability lies in the improper management of object lifetimes within the JavaScript engine's stream handling mechanisms. When a ReadableByteStream object is processed in a manner that allows for concurrent access or premature disposal while references remain active, the underlying memory structures can be freed but still referenced by subsequent operations. This creates a classic use-after-free scenario where an attacker could potentially control the execution flow by manipulating the freed memory or triggering exploitable conditions during garbage collection cycles. The vulnerability specifically impacts the Web Streams API implementation and occurs during the handling of asynchronous data operations that involve stream readers and controllers.
The operational impact of this vulnerability extends beyond simple memory corruption, as it creates potential attack vectors for remote code execution. Attackers could leverage this flaw by crafting malicious web content that triggers the specific sequence of operations leading to the use-after-free condition. The vulnerability affects multiple product versions including Firefox versions prior to 120 and Firefox ESR versions prior to 115.5, as well as Thunderbird versions before 115.5.0, indicating a widespread exposure across the Mozilla ecosystem. This vulnerability aligns with CWE-416, which specifically addresses the use of freed memory conditions, and represents a significant concern for organizations relying on these browsers for email and web browsing operations.
Security researchers have identified that this vulnerability could be exploited through web-based attacks, where malicious websites could trigger the problematic code path by creating specific stream operations that lead to the memory management issue. The attack surface is particularly concerning given the widespread use of Firefox and Thunderbird across enterprise and consumer environments, potentially allowing for privilege escalation or data compromise. Organizations should prioritize immediate patching of affected versions, as the vulnerability demonstrates characteristics consistent with advanced persistent threat actors who may be actively exploiting similar issues in the wild. The mitigation strategy should include not only applying the relevant security patches but also implementing network-level protections and monitoring for suspicious web traffic patterns that might indicate exploitation attempts.