CVE-2024-5690 in Firefox
Summary
by MITRE • 06/11/2024
By monitoring the time certain operations take, an attacker could have guessed which external protocol handlers were functional on a user's system. This vulnerability affects Firefox < 127 and Firefox ESR < 115.12.
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Analysis
by VulDB Data Team • 06/18/2025
This vulnerability represents a timing side-channel attack that exploits the temporal characteristics of external protocol handler detection within the Firefox browser. The flaw allows attackers to infer information about a user's system configuration by measuring the execution time of specific operations, specifically those related to external protocol handlers. The vulnerability stems from inconsistent timing behavior when Firefox attempts to determine whether various external handlers are available on the system. When a protocol handler is present and functional, the operation completes with different timing characteristics compared to when it fails or times out due to missing handlers. This timing differential creates a measurable artifact that can be exploited through careful observation and statistical analysis.
The technical implementation of this vulnerability involves Firefox's protocol handler resolution mechanism where the browser performs checks to determine which external applications can handle specific URI schemes. The timing variations occur during the resolution process when the browser either successfully connects to a handler or encounters a timeout when attempting to access a non-existent or disabled handler. Attackers can leverage this information to build a profile of installed applications on the target system, potentially identifying which external protocols are available and functional. This type of vulnerability falls under the category of timing side-channel attacks that are classified as CWE-384 and aligns with ATT&CK technique T1059.007 for process injection and T1082 for system information discovery.
The operational impact of this vulnerability extends beyond simple reconnaissance as it provides attackers with valuable information about the target environment that could be used to craft more sophisticated attacks. An attacker could use this information to identify which applications are installed and potentially exploit other vulnerabilities in those applications or use the knowledge to tailor phishing campaigns that appear more legitimate. The vulnerability affects both regular Firefox releases and the extended support release versions, indicating a widespread impact across different deployment scenarios. The specific versions affected show that this flaw has existed for some time and represents a persistent issue in Firefox's protocol handling implementation. The timing-based approach makes this particularly concerning as it does not require direct access to the system or elevated privileges, making it accessible through web-based attacks.
Mitigation strategies for this vulnerability primarily focus on addressing the timing inconsistencies in protocol handler resolution. Browser vendors should implement consistent timing behavior for all protocol handler checks regardless of whether the handler is present or absent, effectively eliminating the side-channel information leak. Users should update to Firefox version 127 or Firefox ESR version 115.12, where the vulnerability has been patched. Additionally, administrators can implement network-level mitigations such as restricting access to external protocol handlers through content security policies or browser configuration settings. The patch likely involves modifying the protocol handler detection logic to ensure that all operations complete within similar timeframes, preventing attackers from inferring system state through timing measurements. Organizations should also consider implementing monitoring for suspicious timing patterns in their network traffic analysis to detect potential exploitation attempts. This vulnerability underscores the importance of considering side-channel attack vectors during security reviews and highlights the need for consistent timing behavior in security-sensitive operations as recommended by security standards and best practices.