CVE-2019-9148 in Mailvelope
Summary
by MITRE
Mailvelope prior to 3.3.0 accepts or operates with invalid PGP public keys: Mailvelope allows importing keys that contain users without a valid self-certification. Keys that are obviously invalid are not rejected during import. An attacker that is able to get a victim to import a manipulated key could claim to have signed a message that originates from another person.
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Analysis
by VulDB Data Team • 10/24/2023
The vulnerability described in CVE-2019-9148 represents a critical flaw in the Mailvelope email encryption extension that affected versions prior to 330. This issue stems from insufficient validation of PGP public keys during the import process, creating a pathway for malicious actors to manipulate cryptographic identity verification. The vulnerability specifically targets the OpenPGP standard implementation within Mailvelope, where the software fails to properly verify self-certifications that are fundamental to establishing trust in PGP key infrastructure. According to CWE-290, this weakness falls under authentication bypass due to improper validation of certificate chains, while ATT&CK technique T1556.002 addresses the manipulation of credentials and authentication tokens through certificate manipulation.
The technical flaw manifests when Mailvelope processes PGP keys that contain user IDs without proper self-certifications, which are essential cryptographic proofs that demonstrate the key owner's claim to a particular identity. During the import process, the extension does not adequately validate that each user ID within a key has been properly signed by the corresponding private key, allowing malformed keys to be accepted into the keyring. This validation failure enables attackers to create malicious keys where they can claim to have signed messages from legitimate users, effectively impersonating those individuals in cryptographic communications.
The operational impact of this vulnerability extends beyond simple message forgery to encompass a complete breakdown of trust in the PGP key infrastructure. When a victim imports a manipulated key, they may unknowingly trust forged signatures from the attacker's key, believing that messages were signed by legitimate parties. This creates a significant risk for organizations relying on Mailvelope for secure communications, as it undermines the fundamental security guarantee that PGP provides: the ability to verify message authenticity and sender identity. The vulnerability essentially allows for man-in-the-middle attacks where attackers can masquerade as legitimate users within encrypted email conversations.
Mitigation strategies for CVE-2019-9148 require immediate upgrading to Mailvelope version 3.3.0 or later, which implements proper key validation mechanisms. Security administrators should also conduct comprehensive key reviews of existing keyrings to identify and remove any potentially compromised keys that may have been imported prior to the vulnerability patch. Additionally, organizations should implement key validation policies that require explicit verification of key signatures and self-certifications before trusting any imported keys. The fix addresses the core issue by enforcing strict adherence to OpenPGP standards during key import operations, ensuring that user IDs can only be trusted when they contain valid self-certifications that have been cryptographically verified. This remediation aligns with security best practices outlined in NIST SP 800-57 for cryptographic key management and addresses the broader category of certificate validation failures that can compromise public key infrastructure trust models.