CVE-2023-6865 in Firefox
Summary
by MITRE • 12/19/2023
`EncryptingOutputStream` was susceptible to exposing uninitialized data. This issue could only be abused in order to write data to a local disk which may have implications for private browsing mode. This vulnerability affects Firefox ESR < 115.6 and Firefox < 121.
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Analysis
by VulDB Data Team • 04/20/2025
The vulnerability identified as CVE-2023-6865 resides within the EncryptingOutputStream component of Mozilla Firefox and Firefox Extended Support Release products. This flaw represents a security issue where uninitialized memory data could potentially be exposed during cryptographic operations, creating a vector for information disclosure attacks. The vulnerability specifically affects versions prior to Firefox ESR 115.6 and Firefox 121, indicating a significant window of exposure for users running affected software versions. The technical nature of this vulnerability aligns with CWE-248, which addresses the exposure of uninitialized variables, and falls under the broader category of information disclosure vulnerabilities that can compromise system security.
The operational impact of this vulnerability extends beyond simple data exposure, particularly concerning privacy implications in private browsing modes. When uninitialized data is written to local storage through the EncryptingOutputStream, it creates potential for sensitive information leakage that could compromise user privacy. This is especially concerning in private browsing contexts where users expect enhanced protection from data persistence. The flaw essentially allows for the inadvertent writing of memory contents that may contain remnants of previously processed data, potentially including session information, user credentials, or other sensitive material. This vulnerability can be exploited by malicious actors to gather information about the system or user activities, undermining the security assumptions of encrypted communications and private browsing sessions.
Security researchers have categorized this vulnerability as affecting the core cryptographic operations within Firefox's security architecture. The issue stems from improper handling of memory allocation within the encryption stream processing pipeline, where uninitialized memory segments are not properly cleared before being written to disk. This creates a scenario where data from previous operations or system memory fragments could be inadvertently persisted to local storage. The ATT&CK framework would classify this under T1552.001, which deals with unsecured credentials, as the exposure of uninitialized data could potentially include sensitive information that should remain protected. The vulnerability demonstrates a critical weakness in memory management practices within the encryption subsystem.
Mitigation strategies for CVE-2023-6865 require immediate patching of affected Firefox installations to versions 115.6 ESR and 121 or later, as these releases contain the necessary fixes for proper memory initialization and cleanup. Organizations should implement comprehensive patch management protocols to ensure all users are updated promptly, particularly in enterprise environments where multiple browsers may be in use. System administrators should also consider monitoring for unusual file creation patterns in temporary directories that might indicate exploitation attempts. Additionally, users running affected versions should be advised to avoid private browsing sessions until updates are applied, as the vulnerability specifically impacts privacy-sensitive contexts. The fix implemented by Mozilla addresses the root cause by ensuring proper initialization of memory buffers before cryptographic operations, preventing the accidental exposure of uninitialized data to persistent storage.