CVE-2022-39249 in matrix-js-sdk
Summary
by MITRE • 09/29/2022
Matrix Javascript SDK is the Matrix Client-Server SDK for JavaScript. Prior to version 19.7.0, an attacker cooperating with a malicious homeserver can construct messages appearing to have come from another person. Such messages will be marked with a grey shield on some platforms, but this may be missing in others. This attack is possible due to the matrix-js-sdk implementing a too permissive key forwarding strategy on the receiving end. Starting with version 19.7.0, the default policy for accepting key forwards has been made more strict in the matrix-js-sdk. matrix-js-sdk will now only accept forwarded keys in response to previously issued requests and only from own, verified devices. The SDK now sets a `trusted` flag on the decrypted message upon decryption, based on whether the key used to decrypt the message was received from a trusted source. Clients need to ensure that messages decrypted with a key with `trusted = false` are decorated appropriately, for example, by showing a warning for such messages. This attack requires coordination between a malicious homeserver and an attacker, and those who trust your homeservers do not need a workaround.
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Analysis
by VulDB Data Team • 10/15/2024
The vulnerability described in CVE-2022-39249 affects the Matrix JavaScript SDK, a client-server implementation for the Matrix communication protocol that enables secure messaging and collaboration. This security flaw resides in the key forwarding mechanism implemented within the SDK's receiving end, creating a significant risk for message integrity and user authentication. The vulnerability stems from an overly permissive approach to accepting key forwarding requests from malicious homeservers, allowing attackers to forge messages that appear to originate from legitimate users. This represents a critical compromise of the protocol's trust model, where the cryptographic verification mechanisms fail to properly validate the authenticity of key distribution sources.
The technical implementation flaw manifests in the SDK's handling of cryptographic key forwarding operations, where the system accepts forwarded keys without proper verification of their source legitimacy. The vulnerability specifically targets the key validation process that should ensure keys come from trusted, verified devices within the user's own device list. Prior to version 19.7.0, the SDK would accept key forwards from any source, regardless of whether they originated from the user's own verified devices or from potentially malicious entities. This permissive strategy enabled attackers to craft messages that would display with visual indicators like grey shields, which are typically used to signal trusted communication, but these indicators could be absent on some platforms, creating inconsistent security warnings.
The operational impact of this vulnerability extends beyond simple message forgery to compromise the fundamental security assumptions of the Matrix protocol. An attacker coordinating with a malicious homeserver can successfully manipulate message origins, potentially leading to misinformation campaigns, social engineering attacks, or impersonation attempts. The attack requires specific coordination between the malicious homeserver and the attacker, but once successful, it can undermine user trust in message authenticity. The vulnerability affects users who trust their homeserver operators, as the attack vector relies on compromising the homeserver rather than the client itself. However, the consequences are severe enough that all Matrix users should be aware of this risk, particularly since the visual indicators for trusted messages may not be consistently displayed across different client implementations.
The remediation implemented in version 19.7.0 addresses the core issue by introducing stricter validation policies for key forwarding operations. The updated SDK now requires that forwarded keys be accepted only in response to previously issued requests and only from the user's own verified devices. This change aligns with established security principles for cryptographic key management and implements proper source verification mechanisms. The SDK now sets a trusted flag on decrypted messages based on whether the decryption key originated from a trusted source, creating a clear mechanism for clients to identify potentially compromised communications. This approach follows the principle of least privilege and proper key validation, which are fundamental concepts in cryptographic security design. The implementation also requires client applications to properly handle messages with trusted = false by displaying appropriate warnings, ensuring users are informed about potential security risks. This vulnerability demonstrates the importance of proper key validation in end-to-end encrypted messaging systems and aligns with common security practices outlined in CWE categories related to cryptographic implementation flaws and improper validation of certificates or keys. The solution addresses attack patterns commonly found in the ATT&CK framework under credential access and defense evasion techniques, where attackers attempt to manipulate authentication mechanisms to gain unauthorized access to secure communications.