CVE-2015-2741 in Firefox
Summary
by MITRE
Mozilla Firefox before 39.0, Firefox ESR 38.x before 38.1, and Thunderbird before 38.1 do not enforce key pinning upon encountering an X.509 certificate problem that generates a user dialog, which allows user-assisted man-in-the-middle attackers to bypass intended access restrictions by triggering a (1) expired certificate or (2) mismatched hostname for a domain with pinning enabled.
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Analysis
by VulDB Data Team • 10/22/2024
The vulnerability described in CVE-2015-2741 represents a critical weakness in Mozilla Firefox and Thunderbird browsers that undermines the security of certificate pinning mechanisms. This flaw affects versions prior to Firefox 39.0 and Firefox ESR 38.x before 38.1, as well as Thunderbird versions before 38.1, creating a significant attack surface for man-in-the-middle adversaries who can exploit the improper handling of X.509 certificate validation errors. The vulnerability specifically targets the browser's certificate pinning enforcement system, which is designed to prevent attackers from using fraudulent certificates to impersonate legitimate websites.
The technical flaw manifests when browsers encounter X.509 certificate problems that trigger user dialogs, yet fail to properly enforce certificate pinning restrictions during these interactive scenarios. This behavior creates a window of opportunity for attackers to manipulate the certificate validation process by presenting either expired certificates or certificates with mismatched hostnames for domains that have certificate pinning enabled. The vulnerability stems from the browser's decision to allow users to manually override certificate warnings when pinning should have been enforced, effectively bypassing the security controls that were intended to protect users from certificate-based attacks.
The operational impact of this vulnerability is substantial as it enables user-assisted man-in-the-middle attacks that can compromise the integrity of secure communications. Attackers can leverage this weakness by triggering certificate validation errors that prompt users to make decisions about accepting potentially malicious certificates, while simultaneously bypassing the pinning mechanisms that would normally prevent such connections. This creates a scenario where legitimate security controls are circumvented through user interaction, making the attack vector more accessible and potentially more successful than if the attacker had to directly manipulate the certificate chain without user involvement.
The vulnerability aligns with CWE-295 which describes improper certificate validation, and relates to ATT&CK technique T1552.001 for unsecured credentials and T1046 for network service scanning. Organizations using affected browser versions face increased risk of data interception, session hijacking, and credential theft when users encounter certificate warnings and choose to proceed with connections despite security concerns. The attack requires user interaction but can be significantly amplified through social engineering tactics that encourage users to accept certificate warnings for domains they trust, making the exploitation more likely in real-world scenarios.
Mitigation strategies should focus on immediate browser updates to versions that properly enforce certificate pinning even during user dialog interactions. Security administrators should implement additional monitoring for certificate-related warnings and consider deploying certificate transparency monitoring tools to detect potential pinning bypass attempts. Network security teams should also review and update their security policies to address the increased risk of certificate-based attacks and ensure that user training programs emphasize the importance of not bypassing certificate warnings, particularly for high-value domains that employ certificate pinning.